diff --git a/.cppcheck.suppressions b/.cppcheck.suppressions
index abe53fc0f..a2991396b 100644
--- a/.cppcheck.suppressions
+++ b/.cppcheck.suppressions
@@ -9,6 +9,5 @@ varFuncNullUB
 // warnings are false positives.
 unmatchedSuppression
 
-memleak:src/env_universal_common.cpp
 flockSemanticsWarning:src/env_universal_common.cpp
 flockSemanticsWarning:src/history.cpp
diff --git a/build_tools/iwyu.osx.imp b/build_tools/iwyu.osx.imp
index ee9353021..e00305fed 100644
--- a/build_tools/iwyu.osx.imp
+++ b/build_tools/iwyu.osx.imp
@@ -84,6 +84,7 @@
     { symbol: ["uid_t", "private", "<sys/types.h>", "public"] },
     { symbol: ["gid_t", "private", "<sys/types.h>", "public"] },
     { symbol: ["timeval", "private", "<sys/time.h>", "public"] },
+    { symbol: ["__uint32_t", "private", "<sys/types.h>", "public"] },
     { symbol: ["uint32_t", "private", "<sys/types.h>", "public"] },
     { symbol: ["uint32_t", "private", "<stdint.h>", "public"] },
     { symbol: ["intptr_t", "private", "<stdint.h>", "public"] },
diff --git a/src/autoload.cpp b/src/autoload.cpp
index e63997863..960b586e7 100644
--- a/src/autoload.cpp
+++ b/src/autoload.cpp
@@ -1,17 +1,16 @@
 // The classes responsible for autoloading functions and completions.
 #include "config.h"  // IWYU pragma: keep
 
+#include <assert.h>
 #include <errno.h>
 #include <pthread.h>
-#include <stddef.h>
 #include <sys/stat.h>
 #include <time.h>
 #include <unistd.h>
-#include <wchar.h>
-#include <algorithm>
 #include <memory>
 #include <set>
 #include <string>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
diff --git a/src/autoload.h b/src/autoload.h
index 7a661b4b4..6a395cf08 100644
--- a/src/autoload.h
+++ b/src/autoload.h
@@ -3,7 +3,6 @@
 #define FISH_AUTOLOAD_H
 
 #include <pthread.h>
-#include <stddef.h>
 #include <time.h>
 #include <set>
 
diff --git a/src/builtin_commandline.cpp b/src/builtin_commandline.cpp
index d47d6f534..2ba5b2356 100644
--- a/src/builtin_commandline.cpp
+++ b/src/builtin_commandline.cpp
@@ -3,10 +3,8 @@
 
 #include <assert.h>
 #include <errno.h>
-#include <pthread.h>
 #include <stdlib.h>
 #include <wchar.h>
-#include <cstring>
 
 #include "builtin.h"
 #include "common.h"
diff --git a/src/builtin_string.cpp b/src/builtin_string.cpp
index fc27df8fa..3547e88c8 100644
--- a/src/builtin_string.cpp
+++ b/src/builtin_string.cpp
@@ -15,6 +15,7 @@
 #include <wctype.h>
 #include <algorithm>
 #include <iterator>
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -585,8 +586,7 @@ static int string_match(parser_t &parser, io_streams_t &streams, int argc, wchar
         }
     }
 
-    int rc = matcher->match_count() > 0 ? BUILTIN_STRING_OK : BUILTIN_STRING_NONE;
-    return rc;
+    return matcher->match_count() > 0 ? BUILTIN_STRING_OK : BUILTIN_STRING_NONE;
 }
 
 struct replace_options_t {
@@ -819,8 +819,7 @@ static int string_replace(parser_t &parser, io_streams_t &streams, int argc, wch
         }
     }
 
-    int rc = replacer->replace_count() > 0 ? BUILTIN_STRING_OK : BUILTIN_STRING_NONE;
-    return rc;
+    return replacer->replace_count() > 0 ? BUILTIN_STRING_OK : BUILTIN_STRING_NONE;
 }
 
 /// Given iterators into a string (forward or reverse), splits the haystack iterators
diff --git a/src/builtin_test.cpp b/src/builtin_test.cpp
index 9e5352dcd..2842806dd 100644
--- a/src/builtin_test.cpp
+++ b/src/builtin_test.cpp
@@ -6,13 +6,13 @@
 #include <assert.h>
 #include <errno.h>
 #include <stdarg.h>
-#include <stdio.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <wchar.h>
 #include <memory>
 #include <string>
+#include <type_traits>
 
 #include "builtin.h"
 #include "common.h"
@@ -234,7 +234,7 @@ class combining_expression : public expression {
 
     combining_expression(token_t tok, range_t where, std::vector<unique_ptr<expression>> exprs,
                          std::vector<token_t> combs)
-        : expression(tok, where), subjects(move(exprs)), combiners(move(combs)) {
+        : expression(tok, where), subjects(std::move(exprs)), combiners(std::move(combs)) {
         // We should have one more subject than combiner.
         assert(subjects.size() == combiners.size() + 1);
     }
diff --git a/src/common.cpp b/src/common.cpp
index b03aad111..174cbd575 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -15,6 +15,7 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/time.h>
+#include <sys/types.h>
 #include <termios.h>
 #include <unistd.h>
 #include <wchar.h>
@@ -30,6 +31,7 @@
 #endif
 #include <algorithm>
 #include <memory>  // IWYU pragma: keep
+#include <type_traits>
 
 #include "common.h"
 #include "env.h"
@@ -1783,12 +1785,11 @@ void save_term_foreground_process_group(void) {
 }
 
 void restore_term_foreground_process_group(void) {
-    if (initial_fg_process_group != -1) {
-        // This is called during shutdown and from a signal handler. We don't bother to complain on
-        // failure.
-        if (tcsetpgrp(STDIN_FILENO, initial_fg_process_group) == -1 && errno == ENOTTY) {
-            redirect_tty_output();
-        }
+    if (initial_fg_process_group == -1) return;
+    // This is called during shutdown and from a signal handler. We don't bother to complain on
+    // failure because doing so is unlikely to be noticed.
+    if (tcsetpgrp(STDIN_FILENO, initial_fg_process_group) == -1 && errno == ENOTTY) {
+        redirect_tty_output();
     }
 }
 
diff --git a/src/common.h b/src/common.h
index 964b350c8..91d4396b4 100644
--- a/src/common.h
+++ b/src/common.h
@@ -15,6 +15,7 @@
 #include <memory>
 #include <sstream>
 #include <string>
+#include <type_traits>
 #include <vector>
 
 #include "fallback.h"  // IWYU pragma: keep
diff --git a/src/complete.cpp b/src/complete.cpp
index 3de8c81b1..3b9ae7f72 100644
--- a/src/complete.cpp
+++ b/src/complete.cpp
@@ -12,11 +12,13 @@
 #include <wchar.h>
 #include <wctype.h>
 #include <algorithm>
+#include <functional>
 #include <list>
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
+#include <type_traits>
 #include <utility>
 
 #include "autoload.h"
diff --git a/src/env.cpp b/src/env.cpp
index 106bed009..e1009196c 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -24,6 +24,7 @@
 #include <algorithm>
 #include <map>
 #include <set>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -189,7 +190,6 @@ void var_stack_t::pop() {
     assert(this->top && old_top && !old_top->next);
     assert(this->top != NULL);
 
-    var_table_t::iterator iter;
     for (const auto &entry_pair : old_top->env) {
         const var_entry_t &entry = entry_pair.second;
         if (entry.exportv) {
diff --git a/src/env_universal_common.cpp b/src/env_universal_common.cpp
index e0b5348a9..0047283cf 100644
--- a/src/env_universal_common.cpp
+++ b/src/env_universal_common.cpp
@@ -5,9 +5,16 @@
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
+// We need the sys/file.h for the flock() declaration on Linux but not OS X.
+#include <sys/file.h>  // IWYU pragma: keep
+// We need the ioctl.h header so we can check if SIOCGIFHWADDR is defined by it so we know if we're
+// on a Linux system.
+#include <sys/ioctl.h>  // IWYU pragma: keep
 #include <limits.h>
 #include <netinet/in.h>  // IWYU pragma: keep
+#if !defined(__APPLE__) && !defined(__CYGWIN__)
 #include <pwd.h>
+#endif
 #include <stdlib.h>
 #include <string.h>
 #ifdef __CYGWIN__
@@ -18,16 +25,14 @@
 #endif
 #include <sys/stat.h>
 #include <sys/time.h>  // IWYU pragma: keep
-// We need the sys/file.h for the flock() declaration on Linux but not OS X.
-#include <sys/file.h>  // IWYU pragma: keep
-// We need the ioctl.h header so we can check if SIOCGIFHWADDR is defined by it so we know if we're
-// on a Linux system.
-#include <sys/ioctl.h>  // IWYU pragma: keep
+#include <sys/types.h>  // IWYU pragma: keep
+
 #include <unistd.h>
 #include <wchar.h>
 #include <atomic>
 #include <map>
 #include <string>
+#include <type_traits>
 #include <utility>
 
 #include "common.h"
diff --git a/src/event.cpp b/src/event.cpp
index daac533e8..2b0a68c8c 100644
--- a/src/event.cpp
+++ b/src/event.cpp
@@ -1,12 +1,14 @@
 // Functions for handling event triggers.
 #include "config.h"  // IWYU pragma: keep
 
-#include <assert.h>
 #include <signal.h>
 #include <unistd.h>
+
 #include <algorithm>
+#include <functional>
 #include <memory>
 #include <string>
+#include <type_traits>
 
 #include "common.h"
 #include "event.h"
diff --git a/src/exec.cpp b/src/exec.cpp
index f413e3936..9a8d68a38 100644
--- a/src/exec.cpp
+++ b/src/exec.cpp
@@ -7,21 +7,23 @@
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <signal.h>
-#include <stdio.h>
-#include <string.h>
-#include <unistd.h>
-#include <algorithm>
-#include <vector>
-#ifdef HAVE_SPAWN_H
-#include <spawn.h>
-#endif
-#include <map>
-#include <memory>
-#include <string>
 #ifdef HAVE_SIGINFO_H
 #include <siginfo.h>
 #endif
+#include <signal.h>
+#ifdef HAVE_SPAWN_H
+#include <spawn.h>
+#endif
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <map>
+#include <memory>
+#include <string>
+#include <type_traits>
+#include <vector>
 
 #include "builtin.h"
 #include "common.h"
diff --git a/src/expand.cpp b/src/expand.cpp
index c17f68882..a6bec6e0f 100644
--- a/src/expand.cpp
+++ b/src/expand.cpp
@@ -2,6 +2,7 @@
 // IWYU pragma: no_include <cstddef>
 #include "config.h"
 
+#include <assert.h>
 #include <errno.h>
 #include <pwd.h>
 #include <stdarg.h>
@@ -11,17 +12,13 @@
 #include <unistd.h>
 #include <wchar.h>
 #include <wctype.h>
-#include <algorithm>
 #ifdef HAVE_SYS_SYSCTL_H
 #include <sys/sysctl.h>  // IWYU pragma: keep
 #endif
-#include <assert.h>
-#include <vector>
 #ifdef SunOS
 #include <procfs.h>
 #endif
 #include <stdio.h>
-#include <memory>  // IWYU pragma: keep
 #if __APPLE__
 #include <sys/proc.h>
 #else
@@ -29,6 +26,12 @@
 #include <sys/stat.h>
 #endif
 
+#include <algorithm>
+#include <functional>
+#include <memory>  // IWYU pragma: keep
+#include <type_traits>
+#include <vector>
+
 #include "common.h"
 #include "complete.h"
 #include "env.h"
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index a925c9ba5..7e945b7af 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -24,12 +24,15 @@
 #include <unistd.h>
 #include <wchar.h>
 #include <wctype.h>
+
 #include <algorithm>
 #include <array>
 #include <atomic>
+#include <functional>
 #include <memory>
 #include <set>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "builtin.h"
@@ -1653,9 +1656,9 @@ struct pager_layout_testcase_t {
     size_t width;
     const wchar_t *expected;
 
-    // Run ourselves as a test case
-    // Set our data on the pager, and then check the rendering
-    // We should have one line, and it should have our expected text
+    // Run ourselves as a test case.
+    // Set our data on the pager, and then check the rendering.
+    // We should have one line, and it should have our expected text.
     void run(pager_t &pager) const {
         pager.set_term_size(this->width, 24);
         page_rendering_t rendering = pager.render();
diff --git a/src/highlight.cpp b/src/highlight.cpp
index ac5909613..70003facd 100644
--- a/src/highlight.cpp
+++ b/src/highlight.cpp
@@ -7,11 +7,13 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <wchar.h>
+
 #include <algorithm>
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
+#include <type_traits>
 #include <utility>
 
 #include "builtin.h"
diff --git a/src/highlight.h b/src/highlight.h
index a63cb28dd..bffe6ba13 100644
--- a/src/highlight.h
+++ b/src/highlight.h
@@ -63,7 +63,6 @@ inline highlight_spec_t highlight_make_background(highlight_spec_t val) {
 }
 
 class history_item_t;
-struct file_detection_context_t;
 
 /// Perform syntax highlighting for the shell commands in buff. The result is stored in the color
 /// array as a color_code from the HIGHLIGHT_ enum for each character in buff.
diff --git a/src/history.cpp b/src/history.cpp
index 28e89f2b6..73e511721 100644
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -17,12 +17,15 @@
 #include <unistd.h>
 #include <wchar.h>
 #include <wctype.h>
+
 #include <algorithm>
 #include <atomic>
 #include <cwchar>
+#include <functional>
 #include <iterator>
 #include <map>
 #include <numeric>
+#include <type_traits>
 
 #include "common.h"
 #include "env.h"
diff --git a/src/input.cpp b/src/input.cpp
index 17b5c6dcc..4bdd78544 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -1,6 +1,7 @@
 // Functions for reading a character of input from stdin.
 #include "config.h"
 
+#include <assert.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/src/input_common.cpp b/src/input_common.cpp
index 3d44a7953..08a86534f 100644
--- a/src/input_common.cpp
+++ b/src/input_common.cpp
@@ -4,10 +4,6 @@
 #include <errno.h>
 #include <string.h>
 #include <unistd.h>
-#include <deque>
-#include <list>
-#include <queue>
-#include <utility>
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
 #endif
@@ -16,7 +12,11 @@
 #include <sys/time.h>
 #include <sys/types.h>
 #include <wchar.h>
+
+#include <deque>
+#include <list>
 #include <memory>
+#include <type_traits>
 
 #include "common.h"
 #include "env.h"
diff --git a/src/intern.cpp b/src/intern.cpp
index bd1f60124..2ca0340ac 100644
--- a/src/intern.cpp
+++ b/src/intern.cpp
@@ -1,7 +1,6 @@
 // Library for pooling common strings.
 #include "config.h"  // IWYU pragma: keep
 
-#include <pthread.h>
 #include <stddef.h>
 #include <wchar.h>
 #include <algorithm>
diff --git a/src/iothread.cpp b/src/iothread.cpp
index 5ec7f92e7..7ad527c72 100644
--- a/src/iothread.cpp
+++ b/src/iothread.cpp
@@ -2,7 +2,6 @@
 
 #include <assert.h>
 #include <errno.h>
-#include <fcntl.h>
 #include <limits.h>
 #include <pthread.h>
 #include <signal.h>
diff --git a/src/iothread.h b/src/iothread.h
index b890c4430..8b29370c8 100644
--- a/src/iothread.h
+++ b/src/iothread.h
@@ -3,6 +3,7 @@
 #define FISH_IOTHREAD_H
 
 #include <functional>
+#include <type_traits>
 
 /// Runs a command on a thread.
 ///
diff --git a/src/lru.h b/src/lru.h
index d7632cec8..68b11c2aa 100644
--- a/src/lru.h
+++ b/src/lru.h
@@ -322,6 +322,7 @@ class lru_cache_t {
         // Count iterators
         size_t iter_dist = 0;
         for (const auto &p : *this) {
+            UNUSED(p);
             iter_dist++;
         }
         if (iter_dist != count) {
diff --git a/src/pager.cpp b/src/pager.cpp
index 70373b0af..d84f7913d 100644
--- a/src/pager.cpp
+++ b/src/pager.cpp
@@ -5,6 +5,8 @@
 #include <stddef.h>
 #include <wchar.h>
 #include <wctype.h>
+
+#include <algorithm>
 #include <map>
 #include <numeric>
 #include <vector>
@@ -43,7 +45,7 @@ static size_t divide_round_up(size_t numer, size_t denom) {
     if (numer == 0) return 0;
 
     assert(denom > 0);
-    bool has_rem = (numer % denom) > 0;
+    bool has_rem = (numer % denom) != 0;
     return numer / denom + (has_rem ? 1 : 0);
 }
 
@@ -368,9 +370,7 @@ void pager_t::set_completions(const completion_list_t &raw_completions) {
 
 void pager_t::set_prefix(const wcstring &pref) { prefix = pref; }
 
-void pager_t::set_term_size(int w, int h) {
-    assert(w > 0);
-    assert(h > 0);
+void pager_t::set_term_size(size_t w, size_t h) {
     available_term_width = w;
     available_term_height = h;
 }
@@ -426,7 +426,6 @@ bool pager_t::completion_try_print(size_t cols, const wcstring &prefix, const co
     }
 
     bool print;
-    assert(cols >= 1);
     // Force fit if one column.
     if (cols == 1) {
         width_by_column[0] = std::min(width_by_column[0], term_width);
diff --git a/src/pager.h b/src/pager.h
index 74b9e9ce0..20c5bcf50 100644
--- a/src/pager.h
+++ b/src/pager.h
@@ -131,7 +131,7 @@ class pager_t {
     void set_prefix(const wcstring &pref);
 
     // Sets the terminal width and height.
-    void set_term_size(int w, int h);
+    void set_term_size(size_t w, size_t h);
 
     // Changes the selected completion in the given direction according to the layout of the given
     // rendering. Returns true if the selection changed.
diff --git a/src/parse_execution.cpp b/src/parse_execution.cpp
index 55110d885..7d65622d5 100644
--- a/src/parse_execution.cpp
+++ b/src/parse_execution.cpp
@@ -21,6 +21,7 @@
 #include <algorithm>
 #include <memory>
 #include <string>
+#include <type_traits>
 #include <vector>
 
 #include "builtin.h"
diff --git a/src/parse_tree.cpp b/src/parse_tree.cpp
index eda099ac3..e6372f3a7 100644
--- a/src/parse_tree.cpp
+++ b/src/parse_tree.cpp
@@ -6,9 +6,10 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <wchar.h>
+
 #include <algorithm>
-#include <cwchar>
 #include <string>
+#include <type_traits>
 #include <vector>
 
 #include "common.h"
diff --git a/src/parse_util.cpp b/src/parse_util.cpp
index f0a6177c8..98a0ec65b 100644
--- a/src/parse_util.cpp
+++ b/src/parse_util.cpp
@@ -9,8 +9,10 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <wchar.h>
+
 #include <memory>
 #include <string>
+#include <type_traits>
 
 #include "builtin.h"
 #include "common.h"
diff --git a/src/parser.h b/src/parser.h
index 4baec50b6..2ac09c7d2 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -3,7 +3,11 @@
 #define FISH_PARSER_H
 
 #include <stddef.h>
+
+#include <csignal>
 #include <list>
+#include <memory>
+#include <type_traits>
 #include <vector>
 
 #include "common.h"
diff --git a/src/path.cpp b/src/path.cpp
index 1aa0056ea..ae4be9618 100644
--- a/src/path.cpp
+++ b/src/path.cpp
@@ -12,6 +12,7 @@
 #include <wchar.h>
 
 #include <string>
+#include <type_traits>
 #include <vector>
 
 #include "common.h"
diff --git a/src/proc.cpp b/src/proc.cpp
index 4fcb07e7c..2641aff6c 100644
--- a/src/proc.cpp
+++ b/src/proc.cpp
@@ -7,7 +7,6 @@
 #include "config.h"
 
 #include <errno.h>
-#include <pthread.h>
 #include <signal.h>
 #include <stdio.h>
 #include <sys/wait.h>
diff --git a/src/proc.h b/src/proc.h
index 8aa42f77d..ef2aaa759 100644
--- a/src/proc.h
+++ b/src/proc.h
@@ -11,7 +11,10 @@
 #include <sys/time.h>  // IWYU pragma: keep
 #include <termios.h>
 #include <unistd.h>
+
 #include <list>
+#include <memory>
+#include <vector>
 
 #include "common.h"
 #include "io.h"
diff --git a/src/reader.cpp b/src/reader.cpp
index a12d2b189..1aac55357 100644
--- a/src/reader.cpp
+++ b/src/reader.cpp
@@ -37,6 +37,8 @@
 #include <wctype.h>
 
 #include <algorithm>
+#include <csignal>
+#include <functional>
 #include <memory>
 #include <stack>
 
@@ -791,13 +793,13 @@ void reader_init() {
 
 void reader_destroy() { pthread_key_delete(generation_count_key); }
 
+/// Restore the term mode if we own the terminal. It's important we do this before
+/// restore_foreground_process_group, otherwise we won't think we own the terminal.
 void restore_term_mode() {
-    // Restore the term mode if we own the terminal. It's important we do this before
-    // restore_foreground_process_group, otherwise we won't think we own the terminal.
-    if (getpid() == tcgetpgrp(STDIN_FILENO)) {
-        if (tcsetattr(STDIN_FILENO, TCSANOW, &terminal_mode_on_startup) == -1 && errno == EIO) {
-            redirect_tty_output();
-        }
+    if (getpid() != tcgetpgrp(STDIN_FILENO)) return;
+
+    if (tcsetattr(STDIN_FILENO, TCSANOW, &terminal_mode_on_startup) == -1 && errno == EIO) {
+        redirect_tty_output();
     }
 }
 
diff --git a/src/screen.h b/src/screen.h
index 21622ba8f..3d515a2fb 100644
--- a/src/screen.h
+++ b/src/screen.h
@@ -12,7 +12,10 @@
 #include <assert.h>
 #include <stddef.h>
 #include <sys/stat.h>
+#include <sys/types.h>
+
 #include <algorithm>
+#include <map>
 #include <memory>
 #include <set>
 #include <vector>
diff --git a/src/tokenizer.cpp b/src/tokenizer.cpp
index d39e27bcb..5fecf7f2f 100644
--- a/src/tokenizer.cpp
+++ b/src/tokenizer.cpp
@@ -8,7 +8,9 @@
 #include <unistd.h>
 #include <wchar.h>
 #include <wctype.h>
+
 #include <string>
+#include <type_traits>
 
 #include "common.h"
 #include "fallback.h"  // IWYU pragma: keep
diff --git a/src/wutil.cpp b/src/wutil.cpp
index c989269cd..432fd597a 100644
--- a/src/wutil.cpp
+++ b/src/wutil.cpp
@@ -17,8 +17,8 @@
 #include <unistd.h>
 #include <wchar.h>
 #include <wctype.h>
+
 #include <map>
-#include <memory>
 #include <string>
 
 #include "common.h"