diff --git a/src/gfxinit.cpp b/src/gfxinit.cpp
index cdb1de65ac..1a14d47601 100644
--- a/src/gfxinit.cpp
+++ b/src/gfxinit.cpp
@@ -46,6 +46,9 @@ static const SpriteID * const _landscape_spriteindexes[] = {
 	_landscape_spriteindexes_toyland,
 };
 
+/** file index of first user-added GRF file */
+int _first_user_grf_file_index;
+
 /**
  * Load an old fashioned GRF file.
  * @param filename   The name of the file to open.
@@ -238,6 +241,8 @@ static void LoadSpriteTables()
 
 	LoadNewGRF(SPR_NEWGRFS_BASE, i);
 
+	_first_user_grf_file_index = i + 1;
+
 	/* Free and remove the top element. */
 	delete master;
 	_grfconfig = top;
diff --git a/src/rail_cmd.cpp b/src/rail_cmd.cpp
index ce59e3758d..bdae420d15 100644
--- a/src/rail_cmd.cpp
+++ b/src/rail_cmd.cpp
@@ -35,6 +35,7 @@
 #include "object_map.h"
 #include "tracerestrict.h"
 #include "programmable_signals.h"
+#include "spritecache.h"
 
 #include "table/strings.h"
 #include "table/railtypes.h"
@@ -2003,6 +2004,8 @@ static void DrawSingleSignal(TileIndex tile, const RailtypeInfo *rti, Track trac
 		sprite = SPR_PROGSIGNAL_BASE + 16 + image * 2 + condition;
 		is_custom_sprite = false;
 	}
+	extern uint _first_user_grf_file_index;
+	if (!is_custom_sprite) is_custom_sprite = (GetOriginFileSlot(sprite) >= _first_user_grf_file_index);
 
 	if (!is_custom_sprite && variant == SIG_ELECTRIC && IsRestrictedSignal(tile) && GetExistingTraceRestrictProgram(tile, track) != NULL) {
 		if (type == SIGTYPE_PBS || type == SIGTYPE_PBS_ONEWAY) {