diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -30,6 +30,7 @@
 #include "../hotkeys.h"
 
 #include "ai.hpp"
+#include "ai_gui.hpp"
 #include "../script/api/script_log.hpp"
 #include "ai_config.hpp"
 #include "ai_info.hpp"
diff --git a/src/airport_gui.cpp b/src/airport_gui.cpp
--- a/src/airport_gui.cpp
+++ b/src/airport_gui.cpp
@@ -27,6 +27,7 @@
 #include "core/geometry_func.hpp"
 #include "hotkeys.h"
 #include "vehicle_func.h"
+#include "gui.h"
 
 #include "widgets/airport_widget.h"
 
diff --git a/src/dock_gui.cpp b/src/dock_gui.cpp
--- a/src/dock_gui.cpp
+++ b/src/dock_gui.cpp
@@ -25,6 +25,7 @@
 #include "tilehighlight_func.h"
 #include "company_base.h"
 #include "hotkeys.h"
+#include "gui.h"
 
 #include "widgets/dock_widget.h"
 
diff --git a/src/rail_gui.cpp b/src/rail_gui.cpp
--- a/src/rail_gui.cpp
+++ b/src/rail_gui.cpp
@@ -33,6 +33,7 @@
 #include "engine_base.h"
 #include "vehicle_func.h"
 #include "zoom_func.h"
+#include "rail_gui.h"
 
 #include "station_map.h"
 #include "tunnelbridge_map.h"
@@ -1874,7 +1875,7 @@ static void SetDefaultRailGui()
  * @param p needed to be called when a setting changes
  * @return success, needed for settings
  */
-bool ResetSignalVariant(int32 p = 0)
+bool ResetSignalVariant(int32 p)
 {
 	SignalVariant new_variant = (_cur_year < _settings_client.gui.semaphore_build_before ? SIG_SEMAPHORE : SIG_ELECTRIC);
 
diff --git a/src/terraform_gui.cpp b/src/terraform_gui.cpp
--- a/src/terraform_gui.cpp
+++ b/src/terraform_gui.cpp
@@ -31,6 +31,7 @@
 #include "object.h"
 #include "hotkeys.h"
 #include "engine_base.h"
+#include "terraform_gui.h"
 
 #include "widgets/terraform_widget.h"