diff --git a/src/about.cpp b/src/about.cpp
index b5ec23db954..0ca673eb6f2 100644
--- a/src/about.cpp
+++ b/src/about.cpp
@@ -41,7 +41,7 @@ namespace about
 
 // Given a vector of strings, and a config representing an [about] section,
 // add all the credits lines from the about section to the list of strings.
-void add_lines(std::vector<std::string> &res, config const &c) {
+static void add_lines(std::vector<std::string> &res, config const &c) {
 	std::string title=c["title"];
 	if(title.size()) {
 		title = N_("+" + title);
diff --git a/src/dialogs.cpp b/src/dialogs.cpp
index c8629e43aa9..c9f20758928 100644
--- a/src/dialogs.cpp
+++ b/src/dialogs.cpp
@@ -1161,7 +1161,7 @@ void campaign_preview_pane::draw_contents()
 	}
 }
 
-network::connection network_data_dialog(display& disp, const std::string& msg, config& cfg, network::connection connection_num, network::statistics (*get_stats)(network::connection handle))
+static network::connection network_data_dialog(display& disp, const std::string& msg, config& cfg, network::connection connection_num, network::statistics (*get_stats)(network::connection handle))
 {
 #ifdef USE_TINY_GUI
 	const size_t width = 200;
diff --git a/src/editor/editor_palettes.cpp b/src/editor/editor_palettes.cpp
index 6fcffcf0b65..4efe1e3a7f2 100644
--- a/src/editor/editor_palettes.cpp
+++ b/src/editor/editor_palettes.cpp
@@ -34,7 +34,7 @@
 
 namespace map_editor {
 
-bool is_invalid_terrain(t_translation::t_terrain c) {
+static bool is_invalid_terrain(t_translation::t_terrain c) {
 	return (c == t_translation::VOID_TERRAIN || c == t_translation::FOGGED);
 }
 
diff --git a/src/game_events.cpp b/src/game_events.cpp
index 501fdf48b93..e3b35ce81d7 100644
--- a/src/game_events.cpp
+++ b/src/game_events.cpp
@@ -166,7 +166,7 @@ game_state* get_state_of_game()
 	return state_of_game;
 }
 
-bool internal_conditional_passed(const unit_map* units,
+static bool internal_conditional_passed(const unit_map* units,
                         const vconfig cond, bool& backwards_compat)
 {
 
diff --git a/src/gamestatus.cpp b/src/gamestatus.cpp
index 414edd5f33b..908fb06e63d 100644
--- a/src/gamestatus.cpp
+++ b/src/gamestatus.cpp
@@ -799,7 +799,7 @@ void read_save_file(const std::string& name, config& cfg, std::string* error_log
 	}
 }
 
-void copy_era(config &cfg)
+static void copy_era(config &cfg)
 {
 	if (cfg.child("replay_start")
 		&& cfg.child("replay_start")->child("era")
diff --git a/src/hotkeys.cpp b/src/hotkeys.cpp
index 522710b2341..e17aa6b55d1 100644
--- a/src/hotkeys.cpp
+++ b/src/hotkeys.cpp
@@ -473,7 +473,8 @@ hotkey_item& get_hotkey(const SDL_KeyboardEvent& event)
 #endif
 			);
 }
-void _get_visible_hotkey_itor(int index, std::vector<hotkey_item>::iterator& itor)
+
+static void _get_visible_hotkey_itor(int index, std::vector<hotkey_item>::iterator& itor)
 {
 	int counter = 0;
 	for (itor = hotkeys_.begin(); itor != hotkeys_.end(); ++itor) {
diff --git a/src/playcampaign.cpp b/src/playcampaign.cpp
index 2ce34e75b0b..9550abd6aff 100644
--- a/src/playcampaign.cpp
+++ b/src/playcampaign.cpp
@@ -121,7 +121,7 @@ static void clean_saves(const std::string &label)
 	}
 }
 
-LEVEL_RESULT playsingle_scenario(const config& game_config,
+static LEVEL_RESULT playsingle_scenario(const config& game_config,
 		const config* level, display& disp, game_state& state_of_game,
 		const std::vector<config*>& story, upload_log& log, bool skip_replay)
 {
@@ -153,7 +153,7 @@ LEVEL_RESULT playsingle_scenario(const config& game_config,
 }
 
 
-LEVEL_RESULT playmp_scenario(const config& game_config,
+static LEVEL_RESULT playmp_scenario(const config& game_config,
 		config const* level, display& disp, game_state& state_of_game,
 		const config::child_list& story, upload_log& log, bool skip_replay,
 		io_type_t& io_type)
diff --git a/src/serialization/string_utils.cpp b/src/serialization/string_utils.cpp
index 17c3112902f..e5cf9c7e6d4 100644
--- a/src/serialization/string_utils.cpp
+++ b/src/serialization/string_utils.cpp
@@ -406,7 +406,7 @@ bool string_bool(const std::string& str, bool def) {
 	return def;
 }
 
-bool is_username_char(char c) {
+static bool is_username_char(char c) {
 	return ((c == '_') || (c == '-'));
 }
 
@@ -477,7 +477,7 @@ bool word_completion(std::string& text, std::vector<std::string>& wordlist) {
 	return text_start;
 }
 
-bool is_word_boundary(char c) {
+static bool is_word_boundary(char c) {
 	return (c == ' ' || c == ',' || c == ':' || c == '\'' || c == '"' || c == '-');
 }
 
@@ -612,7 +612,7 @@ std::vector< std::pair< int, int > > parse_ranges(std::string const &str)
 	return to_return;
 }
 
-int byte_size_from_utf8_first(unsigned char ch)
+static int byte_size_from_utf8_first(unsigned char ch)
 {
 	int count;
 
diff --git a/src/server/metrics.cpp b/src/server/metrics.cpp
index b0e608d56c8..a54db38a7ef 100644
--- a/src/server/metrics.cpp
+++ b/src/server/metrics.cpp
@@ -23,12 +23,12 @@
 #include <time.h>
 #include <iostream>
 
-bool operator<(const metrics::sample& s, const simple_wml::string_span& name)
+static bool operator<(const metrics::sample& s, const simple_wml::string_span& name)
 {
 	return s.name < name;
 }
 
-bool operator<(const simple_wml::string_span& name, const metrics::sample& s)
+static bool operator<(const simple_wml::string_span& name, const metrics::sample& s)
 {
 	return name < s.name;
 }
diff --git a/src/server/server.cpp b/src/server/server.cpp
index 99bc6554deb..6ef2cdc3c54 100644
--- a/src/server/server.cpp
+++ b/src/server/server.cpp
@@ -91,18 +91,18 @@ clock_t get_cpu_time(bool active) {
 
 sig_atomic_t config_reload = 0;
 
-void reload_config(int signal) {
+static void reload_config(int signal) {
 	assert(signal == SIGHUP);
 	config_reload = 1;
 }
 
-void exit_sigint(int signal) {
+static void exit_sigint(int signal) {
 	assert(signal == SIGINT);
 	LOG_SERVER << "SIGINT caught, exiting without cleanup immediately.\n";
 	exit(1);
 }
 
-void exit_sigterm(int signal) {
+static void exit_sigterm(int signal) {
 	assert(signal == SIGTERM);
 	LOG_SERVER << "SIGTERM caught, exiting without cleanup immediately.\n";
 	exit(1);
diff --git a/src/sound.cpp b/src/sound.cpp
index 2340a21262f..4fdf5db2f6b 100644
--- a/src/sound.cpp
+++ b/src/sound.cpp
@@ -507,7 +507,7 @@ void play_music()
 	fadingout_time=current_track.ms_after;
 }
 
-void play_new_music()
+static void play_new_music()
 {
 	music_start_time = 0; //reset status: no start time
 	want_new_music = true;
diff --git a/src/unit_abilities.cpp b/src/unit_abilities.cpp
index 559722dd356..c8bcc26c7d2 100644
--- a/src/unit_abilities.cpp
+++ b/src/unit_abilities.cpp
@@ -102,7 +102,7 @@ A poisoned unit cannot be cured of its poison by a healer, and must seek the car
 
 namespace unit_abilities {
 
-bool affects_side(const config& cfg, const std::vector<team>& teams, size_t side, size_t other_side)
+static bool affects_side(const config& cfg, const std::vector<team>& teams, size_t side, size_t other_side)
 {
 	if (side == other_side)
 		return utils::string_bool(cfg["affect_allies"], true);