diff --git a/src/builtin_commandline.h b/src/builtin_commandline.h
index 8b4d3d31d..38e841b82 100644
--- a/src/builtin_commandline.h
+++ b/src/builtin_commandline.h
@@ -5,6 +5,9 @@
 #include <cstring>
 #include <cwchar>
 
+#include "io.h"
+#include "maybe.h"
+
 class parser_t;
 
 maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
diff --git a/src/builtin_complete.h b/src/builtin_complete.h
index bb7097f49..70cc0a7b4 100644
--- a/src/builtin_complete.h
+++ b/src/builtin_complete.h
@@ -5,6 +5,9 @@
 #include <cstring>
 #include <cwchar>
 
+#include "io.h"
+#include "maybe.h"
+
 class parser_t;
 
 maybe_t<int> builtin_complete(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
diff --git a/src/builtin_jobs.h b/src/builtin_jobs.h
index 5d4f1e0a8..36aadea89 100644
--- a/src/builtin_jobs.h
+++ b/src/builtin_jobs.h
@@ -5,6 +5,9 @@
 #include <cstring>
 #include <cwchar>
 
+#include "io.h"
+#include "maybe.h"
+
 class parser_t;
 
 maybe_t<int> builtin_jobs(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
diff --git a/src/builtin_printf.h b/src/builtin_printf.h
index c724fde3d..9303cc2cd 100644
--- a/src/builtin_printf.h
+++ b/src/builtin_printf.h
@@ -5,6 +5,9 @@
 #include <cstring>
 #include <cwchar>
 
+#include "io.h"
+#include "maybe.h"
+
 class parser_t;
 
 maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
diff --git a/src/builtin_set_color.h b/src/builtin_set_color.h
index 1a8dd0cce..e2ebea467 100644
--- a/src/builtin_set_color.h
+++ b/src/builtin_set_color.h
@@ -5,6 +5,9 @@
 #include <cstring>
 #include <cwchar>
 
+#include "io.h"
+#include "maybe.h"
+
 class parser_t;
 
 maybe_t<int> builtin_set_color(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
diff --git a/src/builtin_string.h b/src/builtin_string.h
index 224873405..2d0b4babc 100644
--- a/src/builtin_string.h
+++ b/src/builtin_string.h
@@ -5,6 +5,9 @@
 #include <cstring>
 #include <cwchar>
 
+#include "maybe.h"
+#include "io.h"
+
 class parser_t;
 
 maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
diff --git a/src/builtin_ulimit.h b/src/builtin_ulimit.h
index a9d449d50..9c584f685 100644
--- a/src/builtin_ulimit.h
+++ b/src/builtin_ulimit.h
@@ -5,6 +5,8 @@
 #include <cstring>
 #include <cwchar>
 
+#include "io.h"
+
 class parser_t;
 
 maybe_t<int> builtin_ulimit(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
diff --git a/src/complete.h b/src/complete.h
index 04d06a57f..abd27035a 100644
--- a/src/complete.h
+++ b/src/complete.h
@@ -46,7 +46,7 @@ enum {
     /// This completion looks to have the same string as an existing argument.
     COMPLETE_DUPLICATES_ARGUMENT = 1 << 7
 };
-typedef int complete_flags_t;
+using complete_flags_t = int;
 
 /// std::function which accepts a completion string and returns its description.
 using description_func_t = std::function<wcstring(const wcstring &)>;
diff --git a/src/enum_set.h b/src/enum_set.h
index f0d37e146..1c9e67442 100644
--- a/src/enum_set.h
+++ b/src/enum_set.h
@@ -121,7 +121,7 @@ class enum_iter_t {
             return *this;
         }
 
-        iterator_t operator++(int) {
+        const iterator_t operator++(int) {
             auto res = *this;
             v_ += 1;
             return res;
diff --git a/src/fallback.h b/src/fallback.h
index a3fc8c489..e6f0743c0 100644
--- a/src/fallback.h
+++ b/src/fallback.h
@@ -54,9 +54,9 @@ int fish_mkstemp_cloexec(char *);
 /// expects a int (*func)(int) as its last parameter. tputs_arg_t is defined to always be what tputs
 /// expects. Hopefully.
 #if defined(NCURSES_VERSION) || defined(__NetBSD__)
-typedef int tputs_arg_t;
+using tputs_arg_t = int;
 #else
-typedef char tputs_arg_t;
+using tputs_arg_t = char;
 #endif
 
 #ifndef HAVE_WINSIZE
diff --git a/src/fish_version.cpp b/src/fish_version.cpp
index da8bd4ea8..266c114e4 100644
--- a/src/fish_version.cpp
+++ b/src/fish_version.cpp
@@ -9,7 +9,7 @@
 // FISH_BUILD_VERSION="2.7.1-62-gc0480092-dirty"
 // Arrange for it to become a variable.
 static const char *const
-#include "FISH-BUILD-VERSION-FILE"
+#include "../FISH-BUILD-VERSION-FILE"
     ;
 #endif
 
diff --git a/src/lru.h b/src/lru.h
index c1f01c96b..f6eac3265 100644
--- a/src/lru.h
+++ b/src/lru.h
@@ -270,7 +270,7 @@ class lru_cache_t {
         const lru_link_t *node;
 
        public:
-        typedef std::pair<const wcstring &, const Contents &> value_type;
+        using value_type = std::pair<const wcstring &, const Contents &>;
 
         explicit iterator(const lru_link_t *val) : node(val) {}
         void operator++() { node = node->prev; }
diff --git a/src/output.h b/src/output.h
index 4f25283c5..91e5d9a95 100644
--- a/src/output.h
+++ b/src/output.h
@@ -123,7 +123,7 @@ rgb_color_t parse_color(const env_var_t &var, bool is_background);
 
 /// Sets what colors are supported.
 enum { color_support_term256 = 1 << 0, color_support_term24bit = 1 << 1 };
-typedef unsigned int color_support_t;
+using color_support_t = unsigned int;
 color_support_t output_get_color_support();
 void output_set_color_support(color_support_t val);
 
diff --git a/src/postfork.h b/src/postfork.h
index 785cb54ba..372d6b0df 100644
--- a/src/postfork.h
+++ b/src/postfork.h
@@ -55,7 +55,7 @@ void safe_report_exec_error(int err, const char *actual_cmd, const char *const *
 
 #if FISH_USE_POSIX_SPAWN
 /// A RAII type which wraps up posix_spawn's data structures.
-class posix_spawner_t : noncopyable_t, nonmovable_t {
+class posix_spawner_t : maybe_detail::noncopyable_t, maybe_detail::noncopyable_t {
    public:
     /// Attempt to construct from a job and dup2 list.
     /// The caller must check the error function, as this may fail.
diff --git a/src/signal.cpp b/src/signal.cpp
index b5334a382..a5cea961d 100644
--- a/src/signal.cpp
+++ b/src/signal.cpp
@@ -2,13 +2,14 @@
 #include "config.h"  // IWYU pragma: keep
 
 #include <errno.h>
-#include <signal.h>
 #include <stdio.h>
 #ifdef HAVE_SIGINFO_H
 #include <siginfo.h>
 #endif
 #include <pthread.h>
 
+#include <csignal>
+
 #include "common.h"
 #include "event.h"
 #include "fallback.h"  // IWYU pragma: keep
diff --git a/src/signal.h b/src/signal.h
index 99c318646..7b9d513db 100644
--- a/src/signal.h
+++ b/src/signal.h
@@ -2,7 +2,8 @@
 #ifndef FISH_SIGNALH
 #define FISH_SIGNALH
 
-#include <signal.h>
+#include <cstdint>
+#include <csignal>
 
 /// Get the integer signal value representing the specified signal, or -1 of no signal was found.
 int wcs2sig(const wchar_t *str);
diff --git a/src/tokenizer.h b/src/tokenizer.h
index efe614eb3..aaa139f3f 100644
--- a/src/tokenizer.h
+++ b/src/tokenizer.h
@@ -37,7 +37,7 @@ enum class token_type_t {
 /// Make an effort to continue after an error.
 #define TOK_CONTINUE_AFTER_ERROR 8
 
-typedef unsigned int tok_flags_t;
+using tok_flags_t = unsigned int;
 
 enum class tokenizer_error_t {
     none,