diff --git a/functions.h b/functions.h
index ab91f07340..a7237a778c 100644
--- a/functions.h
+++ b/functions.h
@@ -138,6 +138,7 @@ void PlaceTreesRandomly(void);
 void InitializeLandscapeVariables(bool only_constants);
 
 /* misc.c */
+bool IsCustomName(StringID id);
 void DeleteName(StringID id);
 char *GetName(int id, char *buff);
 
diff --git a/misc.c b/misc.c
index 7801a21408..80ef97c725 100644
--- a/misc.c
+++ b/misc.c
@@ -150,9 +150,14 @@ void InitializeGame(int mode, uint size_x, uint size_y)
 	ResetObjectToPlace();
 }
 
+bool IsCustomName(StringID id)
+{
+	return GB(id, 11, 5) == 15;
+}
+
 void DeleteName(StringID id)
 {
-	if ((id & 0xF800) == 0x7800) {
+	if (IsCustomName(id)) {
 		memset(_name_array[id & 0x1FF], 0, sizeof(_name_array[id & 0x1FF]));
 	}
 }
diff --git a/order_cmd.c b/order_cmd.c
index b872e9ea2f..8614bb6390 100644
--- a/order_cmd.c
+++ b/order_cmd.c
@@ -823,7 +823,7 @@ void BackupVehicleOrders(const Vehicle *v, BackuppedOrders *bak)
 	bak->service_interval = v->service_interval;
 
 	/* Safe custom string, if any */
-	if ((v->string_id & 0xF800) != 0x7800) {
+	if (!IsCustomName(v->string_id)) {
 		bak->name[0] = '\0';
 	} else {
 		GetName(v->string_id & 0x7FF, bak->name);
diff --git a/vehicle.c b/vehicle.c
index e4b1ddbf78..bccc9a7753 100644
--- a/vehicle.c
+++ b/vehicle.c
@@ -2073,7 +2073,7 @@ static int32 ReplaceVehicle(Vehicle **w, byte flags, int32 total_cost)
 		MoveVehicleCargo(new_v->type == VEH_Train ? GetFirstVehicleInChain(new_v) : new_v, old_v);
 
 		// Get the name of the old vehicle if it has a custom name.
-		if ((old_v->string_id & 0xF800) != 0x7800) {
+		if (!IsCustomName(old_v->string_id)) {
 			vehicle_name[0] = '\0';
 		} else {
 			GetName(old_v->string_id & 0x7FF, vehicle_name);