diff --git a/src/console_cmds.cpp b/src/console_cmds.cpp
--- a/src/console_cmds.cpp
+++ b/src/console_cmds.cpp
@@ -1049,8 +1049,6 @@ DEF_CONSOLE_CMD(ConNewGame)
 	return true;
 }
 
-extern void SwitchToMode(SwitchMode new_mode);
-
 DEF_CONSOLE_CMD(ConRestart)
 {
 	if (argc == 0) {
diff --git a/src/genworld.cpp b/src/genworld.cpp
--- a/src/genworld.cpp
+++ b/src/genworld.cpp
@@ -262,7 +262,6 @@ void HandleGeneratingWorldAbortion()
 
 	if (_gw.thread != NULL) _gw.thread->Exit();
 
-	extern void SwitchToMode(SwitchMode new_mode);
 	SwitchToMode(_switch_mode);
 }
 
diff --git a/src/genworld_gui.cpp b/src/genworld_gui.cpp
--- a/src/genworld_gui.cpp
+++ b/src/genworld_gui.cpp
@@ -42,7 +42,6 @@ enum GenenerateLandscapeWindowMode {
 	GLWM_SCENARIO,  ///< Generate flat land
 };
 
-extern void SwitchToMode(SwitchMode new_mode);
 extern void MakeNewgameSettingsLive();
 
 /**
diff --git a/src/gfx.cpp b/src/gfx.cpp
--- a/src/gfx.cpp
+++ b/src/gfx.cpp
@@ -1700,7 +1700,6 @@ void DrawDirtyBlocks()
 		_modal_progress_paint_mutex->BeginCritical();
 		_modal_progress_work_mutex->BeginCritical();
 
-		extern void SwitchToMode(SwitchMode new_mode);
 		if (_switch_mode != SM_NONE && !HasModalProgress()) {
 			SwitchToMode(_switch_mode);
 			_switch_mode = SM_NONE;
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -38,7 +38,6 @@
 
 static void ShowNetworkStartServerWindow();
 static void ShowNetworkLobbyWindow(NetworkGameList *ngl);
-extern void SwitchToMode(SwitchMode new_mode);
 
 static const StringID _connection_types_dropdown[] = {
 	STR_NETWORK_START_SERVER_LAN_INTERNET,
diff --git a/src/openttd.h b/src/openttd.h
--- a/src/openttd.h
+++ b/src/openttd.h
@@ -77,4 +77,6 @@ void AskExitToGameMenu();
 int ttd_main(int argc, char *argv[]);
 void HandleExitGameRequest();
 
+void SwitchToMode(SwitchMode new_mode);
+
 #endif /* OPENTTD_H */
diff --git a/src/video/dedicated_v.cpp b/src/video/dedicated_v.cpp
--- a/src/video/dedicated_v.cpp
+++ b/src/video/dedicated_v.cpp
@@ -138,7 +138,6 @@ static void *_dedicated_video_mem;
 bool _dedicated_forks;
 
 extern bool SafeLoad(const char *filename, int mode, GameMode newgm, Subdirectory subdir, struct LoadFilter *lf = NULL);
-extern void SwitchToMode(SwitchMode new_mode);
 
 static FVideoDriver_Dedicated iFVideoDriver_Dedicated;