diff --git a/maps/mountain_fortress_v3/ic/functions.lua b/maps/mountain_fortress_v3/ic/functions.lua
index 8e5a10306..d9246461b 100644
--- a/maps/mountain_fortress_v3/ic/functions.lua
+++ b/maps/mountain_fortress_v3/ic/functions.lua
@@ -1097,7 +1097,7 @@ function Public.validate_owner(player, entity)
 end
 
 function Public.create_room_surface(ce, unit_number)
-    surface_name = unit_number_to_surface_name(ce.name, unit_number)
+    local surface_name = unit_number_to_surface_name(ce.name, unit_number)
     if game.surfaces[surface_name] then
         return game.surfaces[surface_name].index
     end
diff --git a/maps/mountain_fortress_v3/icw/functions.lua b/maps/mountain_fortress_v3/icw/functions.lua
index aeab6b1dd..ff4c04dc7 100644
--- a/maps/mountain_fortress_v3/icw/functions.lua
+++ b/maps/mountain_fortress_v3/icw/functions.lua
@@ -565,7 +565,7 @@ function Public.kill_wagon(icw, entity)
 end
 
 function Public.create_room_surface(icw, unit_number)
-    surface_name = unit_number_to_surface_name(unit_number) 
+    local surface_name = unit_number_to_surface_name(unit_number) 
     if game.surfaces[surface_name] then
         return game.surfaces[surface_name]
     end