diff --git a/.clang-tidy b/.clang-tidy
index 75262a658..fd47b8fc5 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -1,5 +1,5 @@
 ---
-Checks:          'clang-diagnostic-*,clang-analyzer-*,cert-*,performance-*,portability-*,modernize-use-auto,modernize-loop-convert,modernize-use-bool-literals,modernize-use-using,hicpp-uppercase-literal-suffix'
+Checks:          'clang-diagnostic-*,clang-analyzer-*,cert-*,performance-*,portability-*,modernize-use-auto,modernize-loop-convert,modernize-use-bool-literals,modernize-use-using,hicpp-uppercase-literal-suffix,readability-make-member-function-const'
 WarningsAsErrors: ''
 HeaderFilterRegex: ''
 AnalyzeTemporaryDtors: false
diff --git a/src/env_universal_common.cpp b/src/env_universal_common.cpp
index 3fab6cabc..423a53953 100644
--- a/src/env_universal_common.cpp
+++ b/src/env_universal_common.cpp
@@ -1288,7 +1288,7 @@ class universal_notifier_named_pipe_t : public universal_notifier_t {
 
     void make_pipe(const wchar_t *test_path);
 
-    void drain_excessive_data() {
+    void drain_excessive_data() const {
         // The pipe seems to have data on it, that won't go away. Read a big chunk out of it. We
         // don't read until it's exhausted, because if someone were to pipe say /dev/null, that
         // would cause us to hang!
diff --git a/src/history_file.cpp b/src/history_file.cpp
index 66cc2f548..75b905bf6 100644
--- a/src/history_file.cpp
+++ b/src/history_file.cpp
@@ -161,7 +161,7 @@ history_item_t history_file_contents_t::decode_item(size_t offset) const {
     return history_item_t{};
 }
 
-maybe_t<size_t> history_file_contents_t::offset_of_next_item(size_t *cursor, time_t cutoff) {
+maybe_t<size_t> history_file_contents_t::offset_of_next_item(size_t *cursor, time_t cutoff) const {
     auto offset = size_t(-1);
     switch (this->type()) {
         case history_type_fish_2_0:
diff --git a/src/history_file.h b/src/history_file.h
index bc5992011..bdd24cfc8 100644
--- a/src/history_file.h
+++ b/src/history_file.h
@@ -29,7 +29,7 @@ class history_file_contents_t {
     /// The cursor should initially be 0.
     /// If cutoff is nonzero, skip items whose timestamp is newer than cutoff.
     /// \return the offset of the next item, or none() on end.
-    maybe_t<size_t> offset_of_next_item(size_t *cursor, time_t cutoff);
+    maybe_t<size_t> offset_of_next_item(size_t *cursor, time_t cutoff) const;
 
     /// Get the file type.
     history_file_type_t type() const { return type_; }
diff --git a/src/signal.cpp b/src/signal.cpp
index c17587cea..e4d1f1d7a 100644
--- a/src/signal.cpp
+++ b/src/signal.cpp
@@ -407,7 +407,7 @@ bool sigint_checker_t::check() {
     return changed;
 }
 
-void sigint_checker_t::wait() {
+void sigint_checker_t::wait() const {
     auto &tm = topic_monitor_t::principal();
     generation_list_t gens{};
     gens[topic_t::sighupint] = this->gen_;
diff --git a/src/signal.h b/src/signal.h
index af284f36c..88bec4c2a 100644
--- a/src/signal.h
+++ b/src/signal.h
@@ -45,7 +45,7 @@ class sigint_checker_t {
     bool check();
 
     /// Wait until a sigint is delivered.
-    void wait();
+    void wait() const;
 };
 
 #endif
diff --git a/src/wgetopt.cpp b/src/wgetopt.cpp
index f64515763..127f8e919 100644
--- a/src/wgetopt.cpp
+++ b/src/wgetopt.cpp
@@ -302,7 +302,7 @@ void wgetopter_t::_update_long_opt(int argc, wchar_t **argv, const struct woptio
 // Find a matching long opt.
 const struct woption *wgetopter_t::_find_matching_long_opt(const struct woption *longopts,
                                                            wchar_t *nameend, int *exact, int *ambig,
-                                                           int *indfound) {
+                                                           int *indfound) const {
     const struct woption *pfound = nullptr;
     int option_index = 0;
 
diff --git a/src/wgetopt.h b/src/wgetopt.h
index ae5ed0b21..496c27285 100644
--- a/src/wgetopt.h
+++ b/src/wgetopt.h
@@ -54,7 +54,7 @@ class wgetopter_t {
     bool _handle_long_opt(int argc, wchar_t **argv, const struct woption *longopts, int *longind,
                           int long_only, int *retval);
     const struct woption *_find_matching_long_opt(const struct woption *longopts, wchar_t *nameend,
-                                                  int *exact, int *ambig, int *indfound);
+                                                  int *exact, int *ambig, int *indfound) const;
     void _update_long_opt(int argc, wchar_t **argv, const struct woption *pfound, wchar_t *nameend,
                           int *longind, int option_index, int *retval);
     bool initialized = false;
diff --git a/src/wutil.cpp b/src/wutil.cpp
index 427260d1d..3eb90c507 100644
--- a/src/wutil.cpp
+++ b/src/wutil.cpp
@@ -206,7 +206,7 @@ dir_t::~dir_t() {
 
 bool dir_t::valid() const { return this->dir != nullptr; }
 
-bool dir_t::read(wcstring &name) { return wreaddir(this->dir, name); }
+bool dir_t::read(wcstring &name) const { return wreaddir(this->dir, name); }
 
 int wstat(const wcstring &file_name, struct stat *buf) {
     const cstring tmp = wcs2string(file_name);
diff --git a/src/wutil.h b/src/wutil.h
index c142e6853..db98b7221 100644
--- a/src/wutil.h
+++ b/src/wutil.h
@@ -173,7 +173,7 @@ struct file_id_t {
 struct dir_t {
     DIR *dir;
     bool valid() const;
-    bool read(wcstring &name);
+    bool read(wcstring &name) const;
     dir_t(const wcstring &path);
     ~dir_t();
 };