diff --git a/src/builtin_set_color.cpp b/src/builtin_set_color.cpp
index a2fcd3ed1..f820a3539 100644
--- a/src/builtin_set_color.cpp
+++ b/src/builtin_set_color.cpp
@@ -60,7 +60,7 @@ static const struct woption long_options[] = {{L"background", required_argument,
                                               {L"print-colors", no_argument, nullptr, 'c'},
                                               {nullptr, 0, nullptr, 0}};
 
-#if __APPLE__
+#ifdef __APPLE__
 static char sitm_esc[] = "\x1B[3m";
 static char ritm_esc[] = "\x1B[23m";
 static char dim_esc[] = "\x1B[2m";
@@ -73,7 +73,7 @@ int builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
 
 // Hack in missing italics and dim capabilities omitted from MacOS xterm-256color terminfo
 // Helps Terminal.app/iTerm
-#if __APPLE__
+#ifdef __APPLE__
     const auto term_prog = parser.vars().get(L"TERM_PROGRAM");
     if (!term_prog.missing_or_empty() &&
         (term_prog->as_string() == L"Apple_Terminal" || term_prog->as_string() == L"iTerm.app")) {
diff --git a/src/common.cpp b/src/common.cpp
index 8271d4d94..d39012065 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -42,7 +42,7 @@
 
 #ifdef __FreeBSD__
 #include <sys/sysctl.h>
-#elif __APPLE__
+#elif defined(__APPLE__)
 #include <mach-o/dyld.h>
 #endif
 
@@ -2219,13 +2219,13 @@ bool valid_func_name(const wcstring &str) {
 std::string get_executable_path(const char *argv0) {
     char buff[PATH_MAX];
 
-#if __APPLE__
+#ifdef __APPLE__
     // On OS X use it's proprietary API to get the path to the executable.
     // This is basically grabbing exec_path after argc, argv, envp, ...: for us
     // https://opensource.apple.com/source/adv_cmds/adv_cmds-163/ps/print.c
     uint32_t buffSize = sizeof buff;
     if (_NSGetExecutablePath(buff, &buffSize) == 0) return std::string(buff);
-#elif __FreeBSD__
+#elif defined(__FreeBSD__)
     // FreeBSD does not have /proc by default, but it can be mounted as procfs via the
     // Linux compatibility layer. Per sysctl(3), passing in a process ID of -1 returns
     // the value for the current process.
diff --git a/src/env_universal_common.cpp b/src/env_universal_common.cpp
index 4be75f9ec..e8ccf229a 100644
--- a/src/env_universal_common.cpp
+++ b/src/env_universal_common.cpp
@@ -48,8 +48,8 @@
 #include "wcstringutil.h"
 #include "wutil.h"
 
-#if __APPLE__
-#define FISH_NOTIFYD_AVAILABLE 1
+#ifdef __APPLE__
+#define FISH_NOTIFYD_AVAILABLE
 #include <notify.h>
 #endif
 
@@ -1186,7 +1186,7 @@ class universal_notifier_shmem_poller_t : public universal_notifier_t {
 
 /// A notifyd-based notifier. Very straightforward.
 class universal_notifier_notifyd_t : public universal_notifier_t {
-#if FISH_NOTIFYD_AVAILABLE
+#ifdef FISH_NOTIFYD_AVAILABLE
     int notify_fd;
     int token;
     std::string name;
@@ -1435,7 +1435,7 @@ class universal_notifier_named_pipe_t : public universal_notifier_t {
 };
 
 universal_notifier_t::notifier_strategy_t universal_notifier_t::resolve_default_strategy() {
-#if FISH_NOTIFYD_AVAILABLE
+#ifdef FISH_NOTIFYD_AVAILABLE
     return strategy_notifyd;
 #elif defined(__CYGWIN__)
     return strategy_shmem_polling;
diff --git a/src/expand.cpp b/src/expand.cpp
index 4473b481f..9983ea856 100644
--- a/src/expand.cpp
+++ b/src/expand.cpp
@@ -16,7 +16,7 @@
 #ifdef SunOS
 #include <procfs.h>
 #endif
-#if __APPLE__
+#ifdef __APPLE__
 #include <sys/time.h>  // Required to build with old SDK versions
 // proc.h needs to be included *after* time.h, this comment stops clang-format from reordering.
 #include <sys/proc.h>
diff --git a/src/fallback.cpp b/src/fallback.cpp
index 92a4bb069..c44e55b37 100644
--- a/src/fallback.cpp
+++ b/src/fallback.cpp
@@ -113,7 +113,7 @@ int fish_mkstemp_cloexec(char *name_template) {
     return wcsncasecmp_fallback(a + 1, b + 1, count - 1);
 }
 
-#if __APPLE__
+#ifdef __APPLE__
 #if __DARWIN_C_LEVEL >= 200809L
 // Note parens avoid the macro expansion.
 wchar_t *wcsdup_use_weak(const wchar_t *a) {
diff --git a/src/fallback.h b/src/fallback.h
index 04f56158c..f9788755b 100644
--- a/src/fallback.h
+++ b/src/fallback.h
@@ -73,7 +73,7 @@ char *tparm_solaris_kludge(char *str, long p1 = 0, long p2 = 0, long p3 = 0, lon
 // these functions only exist on 10.7+.
 //
 // On other platforms, use what's detected at build time.
-#if __APPLE__
+#ifdef __APPLE__
 // Avoid warnings about unknown `clang::weak_import` attribute (e.g. GCC 8.2.0 on macOS 10.10)
 #if __DARWIN_C_LEVEL >= 200809L && __clang__ && __has_attribute(weak_import)
 // We have to explicitly redeclare these as weak, since we are forced to set the MIN_REQUIRED
diff --git a/src/postfork.cpp b/src/postfork.cpp
index 1fbf1641c..42101f208 100644
--- a/src/postfork.cpp
+++ b/src/postfork.cpp
@@ -9,7 +9,7 @@
 
 #include <cstring>
 #include <memory>
-#if FISH_USE_POSIX_SPAWN
+#ifdef FISH_USE_POSIX_SPAWN
 #include <spawn.h>
 #endif
 #include <cwchar>
diff --git a/src/postfork.h b/src/postfork.h
index 91cc37aa8..2e7abc47b 100644
--- a/src/postfork.h
+++ b/src/postfork.h
@@ -40,7 +40,7 @@ pid_t execute_fork();
 void safe_report_exec_error(int err, const char *actual_cmd, const char *const *argv,
                             const char *const *envv);
 
-#if FISH_USE_POSIX_SPAWN
+#ifdef FISH_USE_POSIX_SPAWN
 /// Initializes and fills in a posix_spawnattr_t; on success, the caller should destroy it via
 /// posix_spawnattr_destroy.
 bool fork_actions_make_spawn_properties(posix_spawnattr_t *attr,
diff --git a/src/topic_monitor.cpp b/src/topic_monitor.cpp
index 779c5bffb..7a5fe7816 100644
--- a/src/topic_monitor.cpp
+++ b/src/topic_monitor.cpp
@@ -16,11 +16,11 @@
 // block) and use use select() to poll it.
 #if defined(__has_feature)
 #if __has_feature(thread_sanitizer)
-#define TOPIC_MONITOR_TSAN_WORKAROUND 1
+#define TOPIC_MONITOR_TSAN_WORKAROUND
 #endif
 #endif
-#if __SANITIZE_THREAD__
-#define TOPIC_MONITOR_TSAN_WORKAROUND 1
+#ifdef __SANITIZE_THREAD__
+#define TOPIC_MONITOR_TSAN_WORKAROUND
 #endif
 
 /// Implementation of the principal monitor. This uses new (and leaks) to avoid registering a
@@ -49,7 +49,7 @@ topic_monitor_t::topic_monitor_t() {
     // The read end must block to avoid spinning in await.
     DIE_ON_FAILURE(make_fd_nonblocking(pipes_.write.fd()));
 
-#if TOPIC_MONITOR_TSAN_WORKAROUND
+#ifdef TOPIC_MONITOR_TSAN_WORKAROUND
     DIE_ON_FAILURE(make_fd_nonblocking(pipes_.read.fd()));
 #endif
 }
@@ -144,7 +144,7 @@ generation_list_t topic_monitor_t::await_gens(const generation_list_t &input_gen
             assert(gens == input_gens &&
                    "Generations should not have changed if we are the reader.");
             int fd = pipes_.read.fd();
-#if TOPIC_MONITOR_TSAN_WORKAROUND
+#ifdef TOPIC_MONITOR_TSAN_WORKAROUND
             // Under tsan our notifying pipe is non-blocking, so we would busy-loop on the read()
             // call until data is available (that is, fish would use 100% cpu while waiting for
             // processes). The select prevents that.