diff --git a/src/autoload.cpp b/src/autoload.cpp
index 326279e4e..ade837725 100644
--- a/src/autoload.cpp
+++ b/src/autoload.cpp
@@ -17,7 +17,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// The time before we'll recheck an autoloaded file.
-const int kAutoloadStalenessInterval = 15;
+static const int kAutoloadStalenessInterval = 15;
 
 /// Represents a file that we might want to autoload.
 namespace {
diff --git a/src/builtin.cpp b/src/builtin.cpp
index 07ce3cd70..ed21d9848 100644
--- a/src/builtin.cpp
+++ b/src/builtin.cpp
@@ -224,8 +224,7 @@ static maybe_t<int> builtin_generic(parser_t &parser, io_streams_t &streams, con
 
 // How many bytes we read() at once.
 // Since this is just for counting, it can be massive.
-constexpr int COUNT_CHUNK_SIZE = 512 * 256;
-
+#define COUNT_CHUNK_SIZE (512 * 256)
 /// Implementation of the builtin count command, used to count the number of arguments sent to it.
 static maybe_t<int> builtin_count(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
@@ -414,7 +413,7 @@ static constexpr builtin_data_t builtin_datas[] = {
 };
 ASSERT_SORTED_BY_NAME(builtin_datas);
 
-constexpr int BUILTIN_COUNT = sizeof builtin_datas / sizeof *builtin_datas;
+#define BUILTIN_COUNT (sizeof builtin_datas / sizeof *builtin_datas)
 
 /// Look up a builtin_data_t for a specified builtin
 ///
diff --git a/src/builtins/math.cpp b/src/builtins/math.cpp
index 98d409984..979e13435 100644
--- a/src/builtins/math.cpp
+++ b/src/builtins/math.cpp
@@ -19,7 +19,7 @@
 #include "../wutil.h"  // IWYU pragma: keep
 
 // The maximum number of points after the decimal that we'll print.
-constexpr int kDefaultScale = 6;
+static constexpr int kDefaultScale = 6;
 
 // The end of the range such that every integer is representable as a double.
 // i.e. this is the first value such that x + 1 == x (or == x + 2, depending on rounding mode).
diff --git a/src/builtins/path.cpp b/src/builtins/path.cpp
index aa0fb2fae..8d774fdd8 100644
--- a/src/builtins/path.cpp
+++ b/src/builtins/path.cpp
@@ -34,7 +34,7 @@
 // How many bytes we read() at once.
 // We use PATH_MAX here so we always get at least one path,
 // and so we can automatically detect NULL-separated input.
-constexpr int PATH_CHUNK_SIZE = PATH_MAX;
+#define PATH_CHUNK_SIZE PATH_MAX
 
 static void path_error(io_streams_t &streams, const wchar_t *fmt, ...) {
     streams.err.append(L"path ");
diff --git a/src/builtins/read.cpp b/src/builtins/read.cpp
index 59d509645..e432a03c8 100644
--- a/src/builtins/read.cpp
+++ b/src/builtins/read.cpp
@@ -247,7 +247,7 @@ static int read_interactive(parser_t &parser, wcstring &buff, int nchars, bool s
 /// Bash uses 128 bytes for its chunk size. Very informal testing I did suggested that a smaller
 /// chunk size performed better. However, we're going to use the bash value under the assumption
 /// they've done more extensive testing.
-constexpr int READ_CHUNK_SIZE = 128;
+#define READ_CHUNK_SIZE 128
 
 /// Read from the fd in chunks until we see newline or null, as requested, is seen. This is only
 /// used when the fd is seekable (so not from a tty or pipe) and we're not reading a specific number
diff --git a/src/builtins/string.cpp b/src/builtins/string.cpp
index a8da87554..e1d7a91a8 100644
--- a/src/builtins/string.cpp
+++ b/src/builtins/string.cpp
@@ -34,7 +34,7 @@
 // Empirically determined.
 // This is probably down to some pipe buffer or some such,
 // but too small means we need to call `read(2)` and str2wcstring a lot.
-constexpr int STRING_CHUNK_SIZE = 1024;
+#define STRING_CHUNK_SIZE 1024
 
 namespace {
 
diff --git a/src/builtins/ulimit.cpp b/src/builtins/ulimit.cpp
index d2a29fb35..d6fd2b90e 100644
--- a/src/builtins/ulimit.cpp
+++ b/src/builtins/ulimit.cpp
@@ -81,7 +81,7 @@ static const struct resource_t resource_arr[] = {
 
 /// This is likely to be the same as RLIMIT_INFINITY, but it shouldn't get used
 /// in the same context (that is, compared to the result of a getrlimit call).
-constexpr int RLIMIT_UNKNOWN = -1;
+#define RLIMIT_UNKNOWN -1
 
 /// Get the implicit multiplication factor for the specified resource limit.
 static int get_multiplier(int what) {
diff --git a/src/common.cpp b/src/common.cpp
index ddf8a1ffc..465f5a89f 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -1372,7 +1372,7 @@ static bool unescape_string_internal(const wchar_t *const input, const size_t in
                     if (unescape_special && input_position == 0 &&
                         !std::wcscmp(input, PROCESS_EXPAND_SELF_STR)) {
                         to_append_or_none = PROCESS_EXPAND_SELF;
-                        input_position += const_strlen(PROCESS_EXPAND_SELF_STR) - 1;  // skip over 'self's
+                        input_position += PROCESS_EXPAND_SELF_STR_LEN - 1;  // skip over 'self's
                     }
                     break;
                 }
diff --git a/src/common.h b/src/common.h
index b4a32e643..d6e0e43ff 100644
--- a/src/common.h
+++ b/src/common.h
@@ -55,34 +55,34 @@
 #endif
 
 // Common string type.
-using wcstring = std::wstring;
-using wcstring_list_t = std::vector<wcstring>;
+typedef std::wstring wcstring;
+typedef std::vector<wcstring> wcstring_list_t;
 
 struct termsize_t;
 
 // Highest legal ASCII value.
-constexpr char ASCII_MAX = 127U;
+#define ASCII_MAX 127u
 
 // Highest legal 16-bit Unicode value.
-constexpr uint16_t UCS2_MAX = 0xFFFF;
+#define UCS2_MAX 0xFFFFu
 
 // Highest legal byte value.
-constexpr uint8_t BYTE_MAX = 0xFF;
+#define BYTE_MAX 0xFFu
 
 // Unicode BOM value.
-constexpr uint16_t UTF8_BOM_WCHAR = 0xFEFF;
+#define UTF8_BOM_WCHAR 0xFEFFu
 
 // Use Unicode "noncharacters" for internal characters as much as we can. This
 // gives us 32 "characters" for internal use that we can guarantee should not
 // appear in our input stream. See http://www.unicode.org/faq/private_use.html.
-constexpr wchar_t RESERVED_CHAR_BASE = static_cast<wchar_t>(0xFDD0);
-constexpr wchar_t RESERVED_CHAR_END = static_cast<wchar_t>(0xFDF0);
+#define RESERVED_CHAR_BASE static_cast<wchar_t>(0xFDD0)
+#define RESERVED_CHAR_END static_cast<wchar_t>(0xFDF0)
 // Split the available noncharacter values into two ranges to ensure there are
 // no conflicts among the places we use these special characters.
-constexpr wchar_t EXPAND_RESERVED_BASE = RESERVED_CHAR_BASE;
-constexpr wchar_t EXPAND_RESERVED_END = (EXPAND_RESERVED_BASE + 16);
-constexpr wchar_t WILDCARD_RESERVED_BASE = EXPAND_RESERVED_END;
-constexpr wchar_t WILDCARD_RESERVED_END = (WILDCARD_RESERVED_BASE + 16);
+#define EXPAND_RESERVED_BASE RESERVED_CHAR_BASE
+#define EXPAND_RESERVED_END (EXPAND_RESERVED_BASE + 16)
+#define WILDCARD_RESERVED_BASE EXPAND_RESERVED_END
+#define WILDCARD_RESERVED_END (WILDCARD_RESERVED_BASE + 16)
 // Make sure the ranges defined above don't exceed the range for noncharacters.
 // This is to make sure we didn't do something stupid in subdividing the
 // Unicode range for our needs.
@@ -102,8 +102,8 @@ constexpr wchar_t WILDCARD_RESERVED_END = (WILDCARD_RESERVED_BASE + 16);
 // Note: We don't use the highest 8 bit range (0xF800 - 0xF8FF) because we know
 // of at least one use of a codepoint in that range: the Apple symbol (0xF8FF)
 // on Mac OS X. See http://www.unicode.org/faq/private_use.html.
-constexpr wchar_t ENCODE_DIRECT_BASE = static_cast<wchar_t>(0xF600);
-constexpr wchar_t ENCODE_DIRECT_END = (ENCODE_DIRECT_BASE + 256);
+#define ENCODE_DIRECT_BASE static_cast<wchar_t>(0xF600)
+#define ENCODE_DIRECT_END (ENCODE_DIRECT_BASE + 256)
 
 // NAME_MAX is not defined on Solaris
 #if !defined(NAME_MAX)
@@ -140,7 +140,7 @@ enum {
     UNESCAPE_INCOMPLETE = 1 << 1,      // allow incomplete escape sequences
     UNESCAPE_NO_BACKSLASHES = 1 << 2,  // don't handle backslash escapes
 };
-using unescape_flags_t = unsigned int;
+typedef unsigned int unescape_flags_t;
 
 // Flags for the escape_string() function. These are only applicable when the escape style is
 // "script" (i.e., STRING_STYLE_SCRIPT).
@@ -156,7 +156,7 @@ enum {
     /// Replace nonprintable control characters with Unicode symbols.
     ESCAPE_SYMBOLIC = 1 << 3
 };
-using escape_flags_t = unsigned int;
+typedef unsigned int escape_flags_t;
 
 /// A user-visible job ID.
 using job_id_t = int;
@@ -300,7 +300,7 @@ std::string wcs2string(const wchar_t *in, size_t len);
 void wcs2string_appending(const wchar_t *in, size_t len, std::string *receiver);
 
 // Check if we are running in the test mode, where we should suppress error output
-constexpr const wchar_t TESTS_PROGRAM_NAME[] = L"(ignore)";
+#define TESTS_PROGRAM_NAME L"(ignore)"
 bool should_suppress_stderr_for_tests();
 
 /// Branch prediction hints. Idea borrowed from Linux kernel. Just used for asserts.
@@ -637,7 +637,7 @@ enum {
 
 // Custom hash function used by unordered_map/unordered_set when key is const
 #ifndef CONST_WCSTRING_HASH
-#define CONST_WCSTRING_HASH
+#define CONST_WCSTRING_HASH 1
 namespace std {
 template <>
 struct hash<const wcstring> {
diff --git a/src/complete.h b/src/complete.h
index 6bd4c8c30..2c27e05b4 100644
--- a/src/complete.h
+++ b/src/complete.h
@@ -27,7 +27,7 @@ struct completion_mode_t {
 };
 
 /// Character that separates the completion and description on programmable completions.
-constexpr char PROG_COMPLETE_SEP = L'\t';
+#define PROG_COMPLETE_SEP L'\t'
 
 class parser_t;
 
diff --git a/src/env.cpp b/src/env.cpp
index fda0f7264..85ca447fd 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -38,19 +38,19 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Some configuration path environment variables.
-constexpr const wchar_t FISH_DATADIR_VAR[] = L"__fish_data_dir";
-constexpr const wchar_t FISH_SYSCONFDIR_VAR[] = L"__fish_sysconf_dir";
-constexpr const wchar_t FISH_HELPDIR_VAR[] = L"__fish_help_dir";
-constexpr const wchar_t FISH_BIN_DIR[] = L"__fish_bin_dir";
-constexpr const wchar_t FISH_CONFIG_DIR[] = L"__fish_config_dir";
-constexpr const wchar_t FISH_USER_DATA_DIR[] = L"__fish_user_data_dir";
+#define FISH_DATADIR_VAR L"__fish_data_dir"
+#define FISH_SYSCONFDIR_VAR L"__fish_sysconf_dir"
+#define FISH_HELPDIR_VAR L"__fish_help_dir"
+#define FISH_BIN_DIR L"__fish_bin_dir"
+#define FISH_CONFIG_DIR L"__fish_config_dir"
+#define FISH_USER_DATA_DIR L"__fish_user_data_dir"
 
 /// At init, we read all the environment variables from this array.
 extern char **environ;
 
 /// The character used to delimit path and non-path variables in exporting and in string expansion.
-constexpr wchar_t PATH_ARRAY_SEP = L':';
-constexpr wchar_t NONPATH_ARRAY_SEP = L' ';
+static constexpr wchar_t PATH_ARRAY_SEP = L':';
+static constexpr wchar_t NONPATH_ARRAY_SEP = L' ';
 
 bool curses_initialized = false;
 
diff --git a/src/env_universal_common.cpp b/src/env_universal_common.cpp
index 5aec61715..465ceac67 100644
--- a/src/env_universal_common.cpp
+++ b/src/env_universal_common.cpp
@@ -55,16 +55,16 @@
 #endif  // Haiku
 
 /// Error message.
-constexpr const wchar_t PARSE_ERR[] = L"Unable to parse universal variable message: '%ls'";
+#define PARSE_ERR L"Unable to parse universal variable message: '%ls'"
 
 /// Small note about not editing ~/.fishd manually. Inserted at the top of all .fishd files.
-constexpr const char SAVE_MSG[] = "# This file contains fish universal variable definitions.\n";
+#define SAVE_MSG "# This file contains fish universal variable definitions.\n"
 
 /// Version for fish 3.0
 #define UVARS_VERSION_3_0 "3.0"
 
 // Maximum file size we'll read.
-constexpr size_t k_max_read_size = 16 * 1024 * 1024;
+static constexpr size_t k_max_read_size = 16 * 1024 * 1024;
 
 // Fields used in fish 2.x uvars.
 namespace fish2x_uvars {
@@ -211,11 +211,11 @@ static bool append_file_entry(env_var_t::env_var_flags_t flags, const wcstring &
 }
 
 /// Encoding of a null string.
-constexpr const wchar_t ENV_NULL[] = L"\x1d";
+static const wchar_t *const ENV_NULL = L"\x1d";
 
 /// Character used to separate arrays in universal variables file.
 /// This is 30, the ASCII record separator.
-constexpr const wchar_t UVAR_ARRAY_SEP = 0x1e;
+static const wchar_t UVAR_ARRAY_SEP = 0x1e;
 
 /// Decode a serialized universal variable value into a list.
 static wcstring_list_t decode_serialized(const wcstring &val) {
@@ -869,7 +869,7 @@ void env_universal_t::parse_message_2x_internal(const wcstring &msgstr, var_tabl
 }
 
 /// Maximum length of hostname. Longer hostnames are truncated.
-constexpr int HOSTNAME_LEN = 255;
+#define HOSTNAME_LEN 255
 
 /// Function to get an identifier based on the hostname.
 bool get_hostname_identifier(wcstring &result) {
@@ -898,8 +898,8 @@ class universal_notifier_shmem_poller_t final : public universal_notifier_t {
         uint32_t universal_variable_seed;
     };
 
-constexpr int SHMEM_MAGIC_NUMBER = 0xF154;
-constexpr int SHMEM_VERSION_CURRENT = 1000;
+#define SHMEM_MAGIC_NUMBER 0xF154
+#define SHMEM_VERSION_CURRENT 1000
 
    private:
     long long last_change_time{0};
diff --git a/src/event.h b/src/event.h
index a2275c07d..bbdf7bd30 100644
--- a/src/event.h
+++ b/src/event.h
@@ -19,7 +19,7 @@
 struct io_streams_t;
 
 /// The process id that is used to match any process id.
-constexpr int EVENT_ANY_PID = 0;
+#define EVENT_ANY_PID 0
 
 /// Enumeration of event types.
 enum class event_type_t {
diff --git a/src/expand.cpp b/src/expand.cpp
index c6d1e9825..17af38038 100644
--- a/src/expand.cpp
+++ b/src/expand.cpp
@@ -39,9 +39,9 @@
 
 /// Characters which make a string unclean if they are the first character of the string. See \c
 /// expand_is_clean().
-constexpr const wchar_t UNCLEAN_FIRST[] = L"~%";
+#define UNCLEAN_FIRST L"~%"
 /// Unclean characters. See \c expand_is_clean().
-constexpr const wchar_t UNCLEAN[] = L"$*?\\\"'({})";
+#define UNCLEAN L"$*?\\\"'({})"
 
 static void remove_internal_separator(wcstring *s, bool conv);
 
diff --git a/src/expand.h b/src/expand.h
index 1d4bf7e89..5649abcb4 100644
--- a/src/expand.h
+++ b/src/expand.h
@@ -133,7 +133,8 @@ struct expand_result_t {
 };
 
 /// The string represented by PROCESS_EXPAND_SELF
-constexpr const wchar_t PROCESS_EXPAND_SELF_STR[] = L"%self";
+#define PROCESS_EXPAND_SELF_STR L"%self"
+#define PROCESS_EXPAND_SELF_STR_LEN 5
 
 /// Perform various forms of expansion on in, such as tilde expansion (\~USER becomes the users home
 /// directory), variable expansion (\$VAR_NAME becomes the value of the environment variable
diff --git a/src/fd_monitor.cpp b/src/fd_monitor.cpp
index 298f606d7..de55abd94 100644
--- a/src/fd_monitor.cpp
+++ b/src/fd_monitor.cpp
@@ -14,7 +14,7 @@
 #include "iothread.h"
 #include "wutil.h"
 
-constexpr uint64_t kUsecPerMsec = 1000;
+static constexpr uint64_t kUsecPerMsec = 1000;
 
 fd_monitor_t::fd_monitor_t() = default;
 
diff --git a/src/fds.cpp b/src/fds.cpp
index 7ca57a7a4..0dbae2eb3 100644
--- a/src/fds.cpp
+++ b/src/fds.cpp
@@ -19,9 +19,9 @@
 
 // The first fd in the "high range." fds below this are allowed to be used directly by users in
 // redirections, e.g. >&3
-constexpr int k_first_high_fd = 10;
-constexpr uint64_t  kUsecPerMsec = 1000;
-constexpr uint64_t kUsecPerSec [[gnu::unused]] = 1000 * kUsecPerMsec;
+const int k_first_high_fd = 10;
+static constexpr uint64_t kUsecPerMsec = 1000;
+static constexpr uint64_t kUsecPerSec [[gnu::unused]] = 1000 * kUsecPerMsec;
 
 void autoclose_fd_t::close() {
     if (fd_ < 0) return;
diff --git a/src/fish_indent.cpp b/src/fish_indent.cpp
index 5d135670f..142786608 100644
--- a/src/fish_indent.cpp
+++ b/src/fish_indent.cpp
@@ -56,7 +56,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 
 // The number of spaces per indent isn't supposed to be configurable.
 // See discussion at https://github.com/fish-shell/fish-shell/pull/6790
-constexpr int SPACES_PER_INDENT = 4;
+#define SPACES_PER_INDENT 4
 
 static bool dump_parse_tree = false;
 static int ret = 0;
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index 6ce1e52e6..fa6cc3934 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -121,11 +121,11 @@ static bool should_test_function(const char *func_name, bool default_on = true)
 }
 
 /// The number of tests to run.
-constexpr int ESCAPE_TEST_COUNT = 100000;
+#define ESCAPE_TEST_COUNT 100000
 /// The average length of strings to unescape.
-constexpr int ESCAPE_TEST_LENGTH = 100;
+#define ESCAPE_TEST_LENGTH 100
 /// The highest character number of character to try and escape.
-constexpr int ESCAPE_TEST_CHAR = 4000;
+#define ESCAPE_TEST_CHAR 4000
 
 /// Number of encountered errors.
 static int err_count = 0;
@@ -3928,8 +3928,8 @@ static void test_undo() {
     do_test(line.text() == L"abc");
 }
 
-constexpr int UVARS_PER_THREAD = 8;
-constexpr const wchar_t UVARS_TEST_PATH[] = L"test/fish_uvars_test/varsfile.txt";
+#define UVARS_PER_THREAD 8
+#define UVARS_TEST_PATH L"test/fish_uvars_test/varsfile.txt"
 
 static int test_universal_helper(int x) {
     callback_data_list_t callbacks;
diff --git a/src/highlight.cpp b/src/highlight.cpp
index b870d3b7b..027756236 100644
--- a/src/highlight.cpp
+++ b/src/highlight.cpp
@@ -550,7 +550,7 @@ static void color_string_internal(const wcstring &buffstr, highlight_spec_t base
 
     // Hacky support for %self which must be an unquoted literal argument.
     if (buffstr == PROCESS_EXPAND_SELF_STR) {
-        std::fill_n(colors, const_strlen(PROCESS_EXPAND_SELF_STR), highlight_role_t::operat);
+        std::fill_n(colors, std::wcslen(PROCESS_EXPAND_SELF_STR), highlight_role_t::operat);
         return;
     }
 
diff --git a/src/history.cpp b/src/history.cpp
index 95a6875ad..80876d587 100644
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -52,21 +52,21 @@
 //   Newlines are replaced by \n. Backslashes are replaced by \\.
 
 // This is the history session ID we use by default if the user has not set env var fish_history.
-constexpr const wchar_t DFLT_FISH_HISTORY_SESSION_ID[] = L"fish";
+#define DFLT_FISH_HISTORY_SESSION_ID L"fish"
 
 // When we rewrite the history, the number of items we keep.
-constexpr int HISTORY_SAVE_MAX = 1024 * 256;
+#define HISTORY_SAVE_MAX (1024 * 256)
 
 // Default buffer size for flushing to the history file.
-constexpr int HISTORY_OUTPUT_BUFFER_SIZE = 64 * 1024;
+#define HISTORY_OUTPUT_BUFFER_SIZE (64 * 1024)
 
 // The file access mode we use for creating history files
-constexpr int history_file_mode = 0600;
+static constexpr int history_file_mode = 0600;
 
 // How many times we retry to save
 // Saving may fail if the file is modified in between our opening
 // the file and taking the lock
-constexpr int max_save_tries = 1024;
+static constexpr int max_save_tries = 1024;
 
 namespace {
 
diff --git a/src/input.cpp b/src/input.cpp
index 2af0b1be3..562cf7f33 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -32,7 +32,7 @@
 #include "wutil.h"   // IWYU pragma: keep
 
 /// A name for our own key mapping for nul.
-constexpr const wchar_t k_nul_mapping_name[] = L"nul";
+static const wchar_t *k_nul_mapping_name = L"nul";
 
 /// Struct representing a keybinding. Returned by input_get_mappings.
 struct input_mapping_t {
@@ -72,7 +72,7 @@ struct terminfo_mapping_t {
     terminfo_mapping_t(const wchar_t *name, std::string s) : name(name), seq(std::move(s)) {}
 };
 
-constexpr size_t input_function_count = R_END_INPUT_FUNCTIONS;
+static constexpr size_t input_function_count = R_END_INPUT_FUNCTIONS;
 
 /// Input function metadata. This list should be kept in sync with the key code list in
 /// input_common.h.
diff --git a/src/input.h b/src/input.h
index 27da08aa5..b775ad779 100644
--- a/src/input.h
+++ b/src/input.h
@@ -14,8 +14,8 @@
 #include "input_common.h"
 #include "maybe.h"
 
-constexpr wchar_t FISH_BIND_MODE_VAR[]  = L"fish_bind_mode";
-constexpr wchar_t DEFAULT_BIND_MODE[]= L"default";
+#define FISH_BIND_MODE_VAR L"fish_bind_mode"
+#define DEFAULT_BIND_MODE L"default"
 
 class event_queue_peeker_t;
 class parser_t;
diff --git a/src/input_common.cpp b/src/input_common.cpp
index 0c20af5c6..307af7522 100644
--- a/src/input_common.cpp
+++ b/src/input_common.cpp
@@ -30,7 +30,7 @@
 /// Time in milliseconds to wait for another byte to be available for reading
 /// after \x1B is read before assuming that escape key was pressed, and not an
 /// escape sequence.
-constexpr int WAIT_ON_ESCAPE_DEFAULT = 30;
+#define WAIT_ON_ESCAPE_DEFAULT 30
 static int wait_on_escape_ms = WAIT_ON_ESCAPE_DEFAULT;
 
 input_event_queue_t::input_event_queue_t(int in) : in_(in) {}
diff --git a/src/io.cpp b/src/io.cpp
index 7442702ef..463311c37 100644
--- a/src/io.cpp
+++ b/src/io.cpp
@@ -26,7 +26,7 @@
 #define NOCLOB_ERROR _(L"The file '%ls' already exists")
 
 /// Base open mode to pass to calls to open.
-constexpr int OPEN_MASK = 0666;
+#define OPEN_MASK 0666
 
 /// Provide the fd monitor used for background fillthread operations.
 static fd_monitor_t &fd_monitor() {
diff --git a/src/iothread.cpp b/src/iothread.cpp
index a6958f04b..c9bbe20ee 100644
--- a/src/iothread.cpp
+++ b/src/iothread.cpp
@@ -21,7 +21,7 @@
 #include "maybe.h"
 
 /// We just define a thread limit of 1024.
-constexpr int IO_MAX_THREADS = 1024;
+#define IO_MAX_THREADS 1024
 
 // iothread has a thread pool. Sometimes there's no work to do, but extant threads wait around for a
 // while (on a condition variable) in case new work comes soon. However condition variables are not
@@ -29,9 +29,9 @@ constexpr int IO_MAX_THREADS = 1024;
 // See https://github.com/google/sanitizers/issues/1259
 // When using TSan, disable the wait-around feature.
 #ifdef FISH_TSAN_WORKAROUNDS
-constexpr int IO_WAIT_FOR_WORK_DURATION_MS = 0;
+#define IO_WAIT_FOR_WORK_DURATION_MS 0
 #else
-constexpr int IO_WAIT_FOR_WORK_DURATION_MS = 500;
+#define IO_WAIT_FOR_WORK_DURATION_MS 500
 #endif
 
 using void_function_t = std::function<void()>;
diff --git a/src/pager.cpp b/src/pager.cpp
index 073c71ef2..a5c5ec199 100644
--- a/src/pager.cpp
+++ b/src/pager.cpp
@@ -30,16 +30,16 @@ using comp_t = pager_t::comp_t;
 using comp_info_list_t = std::vector<comp_t>;
 
 /// The minimum width (in characters) the terminal must to show completions at all.
-constexpr int PAGER_MIN_WIDTH = 16;
+#define PAGER_MIN_WIDTH 16
 
 /// Minimum height to show completions
-constexpr int PAGER_MIN_HEIGHT = 4;
+#define PAGER_MIN_HEIGHT 4
 
 /// The maximum number of columns of completion to attempt to fit onto the screen.
-constexpr int PAGER_MAX_COLS = 6;
+#define PAGER_MAX_COLS 6
 
 /// Width of the search field.
-constexpr int PAGER_SEARCH_FIELD_WIDTH = 12;
+#define PAGER_SEARCH_FIELD_WIDTH 12
 
 /// Text we use for the search field.
 #define SEARCH_FIELD_PROMPT _(L"search: ")
diff --git a/src/pager.h b/src/pager.h
index 3ed17db9e..ff74d055b 100644
--- a/src/pager.h
+++ b/src/pager.h
@@ -15,7 +15,7 @@
 
 struct termsize_t;
 
-constexpr size_t PAGER_SELECTION_NONE = static_cast<size_t>(-1);
+#define PAGER_SELECTION_NONE static_cast<size_t>(-1)
 
 /// Represents rendering from the pager.
 class page_rendering_t {
@@ -56,11 +56,11 @@ enum class selection_motion_t {
 };
 
 // The space between adjacent completions.
-constexpr const wchar_t PAGER_SPACER_STRING[] = L"  ";
-constexpr int PAGER_SPACER_STRING_WIDTH = const_strlen(PAGER_SPACER_STRING);
+#define PAGER_SPACER_STRING L"  "
+#define PAGER_SPACER_STRING_WIDTH 2
 
 // How many rows we will show in the "initial" pager.
-constexpr int PAGER_UNDISCLOSED_MAX_ROWS = 4;
+#define PAGER_UNDISCLOSED_MAX_ROWS 4
 
 class pager_t {
     size_t available_term_width{0};
diff --git a/src/parse_constants.h b/src/parse_constants.h
index 94d90eaa7..bd89e6dc5 100644
--- a/src/parse_constants.h
+++ b/src/parse_constants.h
@@ -189,13 +189,13 @@ struct parse_error_t {
     wcstring describe_with_prefix(const wcstring &src, const wcstring &prefix, bool is_interactive,
                                   bool skip_caret) const;
 };
-using parse_error_list_t = std::vector<parse_error_t>;
+typedef std::vector<parse_error_t> parse_error_list_t;
 
 wcstring token_type_user_presentable_description(parse_token_type_t type,
                                                  parse_keyword_t keyword = parse_keyword_t::none);
 
 // Special source_start value that means unknown.
-constexpr size_t SOURCE_LOCATION_UNKNOWN = static_cast<size_t>(-1);
+#define SOURCE_LOCATION_UNKNOWN (static_cast<size_t>(-1))
 
 /// Helper function to offset error positions by the given amount. This is used when determining
 /// errors in a substring of a larger source buffer.
@@ -209,7 +209,7 @@ enum class pipeline_position_t : uint8_t {
 };
 
 /// Maximum number of function calls.
-constexpr int FISH_MAX_STACK_DEPTH = 128;
+#define FISH_MAX_STACK_DEPTH 128
 
 /// Error message on a function that calls itself immediately.
 #define INFINITE_FUNC_RECURSION_ERR_MSG \
diff --git a/src/parse_util.cpp b/src/parse_util.cpp
index 91fa85a04..f62a0e707 100644
--- a/src/parse_util.cpp
+++ b/src/parse_util.cpp
@@ -43,7 +43,7 @@
 #define TIME_IN_PIPELINE_ERR_MSG _(L"The 'time' command may only be at the beginning of a pipeline")
 
 /// Maximum length of a variable name to show in error reports before truncation
-constexpr int var_err_len = 16;
+static constexpr int var_err_len = 16;
 
 int parse_util_lineno(const wcstring &str, size_t offset) {
     // Return the line number of position offset, starting with 1.
diff --git a/src/print_help.cpp b/src/print_help.cpp
index 456b1eb3b..0b2fa3c71 100644
--- a/src/print_help.cpp
+++ b/src/print_help.cpp
@@ -10,14 +10,15 @@
 
 #include "common.h"
 
-constexpr int CMD_LEN = 1024;
-constexpr char HELP_ERR[] = "Could not show help message\n";
+#define CMD_LEN 1024
+
+#define HELP_ERR "Could not show help message\n"
 
 void print_help(const char *c, int fd) {
     char cmd[CMD_LEN];
     int printed = snprintf(cmd, CMD_LEN, "fish -c '__fish_print_help %s >&%d'", c, fd);
 
     if (printed < CMD_LEN && system(cmd) == -1) {
-        write_loop(2, HELP_ERR, const_strlen(HELP_ERR));
+        write_loop(2, HELP_ERR, std::strlen(HELP_ERR));
     }
 }
diff --git a/src/reader.cpp b/src/reader.cpp
index e1e57e291..7c1f1d831 100644
--- a/src/reader.cpp
+++ b/src/reader.cpp
@@ -83,47 +83,47 @@
 
 // Name of the variable that tells how long it took, in milliseconds, for the previous
 // interactive command to complete.
-constexpr const wchar_t ENV_CMD_DURATION[] = L"CMD_DURATION";
+#define ENV_CMD_DURATION L"CMD_DURATION"
 
 /// Maximum length of prefix string when printing completion list. Longer prefixes will be
 /// ellipsized.
-constexpr int PREFIX_MAX_LEN = 9;
+#define PREFIX_MAX_LEN 9
 
 /// A simple prompt for reading shell commands that does not rely on fish specific commands, meaning
 /// it will work even if fish is not installed. This is used by read_i.
-constexpr const wchar_t DEFAULT_PROMPT[] = L"echo -n \"$USER@$hostname $PWD \"'> '";
+#define DEFAULT_PROMPT L"echo -n \"$USER@$hostname $PWD \"'> '"
 
 /// The name of the function that prints the fish prompt.
-constexpr const wchar_t LEFT_PROMPT_FUNCTION_NAME[] = L"fish_prompt";
+#define LEFT_PROMPT_FUNCTION_NAME L"fish_prompt"
 
 /// The name of the function that prints the fish right prompt (RPROMPT).
-constexpr const wchar_t RIGHT_PROMPT_FUNCTION_NAME[] = L"fish_right_prompt";
+#define RIGHT_PROMPT_FUNCTION_NAME L"fish_right_prompt"
 
 /// The name of the function to use in place of the left prompt if we're in the debugger context.
-constexpr const wchar_t DEBUG_PROMPT_FUNCTION_NAME[] = L"fish_breakpoint_prompt";
+#define DEBUG_PROMPT_FUNCTION_NAME L"fish_breakpoint_prompt"
 
 /// The name of the function for getting the input mode indicator.
-constexpr const wchar_t MODE_PROMPT_FUNCTION_NAME[] = L"fish_mode_prompt";
+#define MODE_PROMPT_FUNCTION_NAME L"fish_mode_prompt"
 
 /// The default title for the reader. This is used by reader_readline.
-constexpr const wchar_t DEFAULT_TITLE[] = L"echo (status current-command) \" \" $PWD";
+#define DEFAULT_TITLE L"echo (status current-command) \" \" $PWD"
 
 /// The maximum number of characters to read from the keyboard without repainting. Note that this
 /// readahead will only occur if new characters are available for reading, fish will never block for
 /// more input without repainting.
-constexpr size_t READAHEAD_MAX = 256;
+static constexpr size_t READAHEAD_MAX = 256;
 
 /// When tab-completing with a wildcard, we expand the wildcard up to this many results.
 /// If expansion would exceed this many results, beep and do nothing.
-constexpr size_t TAB_COMPLETE_WILDCARD_MAX_EXPANSION = 256;
+static const size_t TAB_COMPLETE_WILDCARD_MAX_EXPANSION = 256;
 
 /// A mode for calling the reader_kill function. In this mode, the new string is appended to the
 /// current contents of the kill buffer.
-constexpr int KILL_APPEND = 0;
+#define KILL_APPEND 0
 
 /// A mode for calling the reader_kill function. In this mode, the new string is prepended to the
 /// current contents of the kill buffer.
-constexpr int KILL_PREPEND = 1;
+#define KILL_PREPEND 1
 
 enum class jump_direction_t { forward, backward };
 enum class jump_precision_t { till, to };
@@ -169,7 +169,7 @@ static operation_context_t get_bg_context(const std::shared_ptr<environment_t> &
 /// typed. But we do not want it to block forever - e.g. it may hang on determining if an arbitrary
 /// argument is a path. This is how long we'll wait (in milliseconds) before giving up and
 /// performing a no-io syntax highlighting. See #7418, #5912.
-constexpr long kHighlightTimeoutForExecutionMs = 250;
+static constexpr long kHighlightTimeoutForExecutionMs = 250;
 
 /// Get the debouncer for autosuggestions and background highlighting.
 /// These are deliberately leaked to avoid shutdown dtor registration.
diff --git a/src/screen.cpp b/src/screen.cpp
index 6bec1292b..30e27421b 100644
--- a/src/screen.cpp
+++ b/src/screen.cpp
@@ -45,7 +45,7 @@
 #include "termsize.h"
 
 /// The number of characters to indent new blocks.
-constexpr uint32_t INDENT_STEP = 4U;
+#define INDENT_STEP 4u
 
 /// RAII class to begin and end buffering around an outputter.
 namespace {
diff --git a/src/tokenizer.h b/src/tokenizer.h
index 06c15124c..3fd12466f 100644
--- a/src/tokenizer.h
+++ b/src/tokenizer.h
@@ -26,17 +26,17 @@ enum class token_type_t : uint8_t {
 
 /// Flag telling the tokenizer to accept incomplete parameters, i.e. parameters with mismatching
 /// parenthesis, etc. This is useful for tab-completion.
-constexpr int TOK_ACCEPT_UNFINISHED =  1;
+#define TOK_ACCEPT_UNFINISHED 1
 
 /// Flag telling the tokenizer not to remove comments. Useful for syntax highlighting.
-constexpr int TOK_SHOW_COMMENTS  = 2;
+#define TOK_SHOW_COMMENTS 2
 
 /// Ordinarily, the tokenizer ignores newlines following a newline, or a semicolon. This flag tells
 /// the tokenizer to return each of them as a separate END.
-constexpr int TOK_SHOW_BLANK_LINES = 4;
+#define TOK_SHOW_BLANK_LINES 4
 
 /// Make an effort to continue after an error.
-constexpr int TOK_CONTINUE_AFTER_ERROR = 8;
+#define TOK_CONTINUE_AFTER_ERROR 8
 
 using tok_flags_t = unsigned int;
 
diff --git a/src/utf8.cpp b/src/utf8.cpp
index 96fe74592..dfd031708 100644
--- a/src/utf8.cpp
+++ b/src/utf8.cpp
@@ -24,12 +24,12 @@
 
 #include "common.h"
 
-constexpr char _NXT = 0x80;
-constexpr char _SEQ2 = 0xc0;
-constexpr char _SEQ3 = 0xe0;
-constexpr char _SEQ4 = 0xf0;
+#define _NXT 0x80
+#define _SEQ2 0xc0
+#define _SEQ3 0xe0
+#define _SEQ4 0xf0
 
-constexpr uint16_t _BOM = 0xfeff;
+#define _BOM 0xfeff
 
 // We can tweak the following typedef to allow us to simulate Windows-style 16 bit wchar's on Unix.
 using utf8_wchar_t = wchar_t;
diff --git a/src/utf8.h b/src/utf8.h
index ff1197b3c..cfd2a1b2d 100644
--- a/src/utf8.h
+++ b/src/utf8.h
@@ -22,8 +22,8 @@
 
 #include <string>
 
-constexpr int UTF8_IGNORE_ERROR = 0x01;
-constexpr int UTF8_SKIP_BOM = 0x02;
+#define UTF8_IGNORE_ERROR 0x01
+#define UTF8_SKIP_BOM 0x02
 
 /// Convert a string between UTF8 and UCS-2/4 (depending on size of wchar_t). Returns true if
 /// successful, storing the result of the conversion in *result*.
diff --git a/src/wutil.h b/src/wutil.h
index ef9a0d1b4..84a77e668 100644
--- a/src/wutil.h
+++ b/src/wutil.h
@@ -176,7 +176,7 @@ struct dir_t {
 };
 
 #ifndef HASH_FILE_ID
-#define HASH_FILE_ID
+#define HASH_FILE_ID 1
 namespace std {
 template <>
 struct hash<file_id_t> {