diff --git a/src/mklev.c b/src/mklev.c
index add7d733d..d0b30967a 100644
--- a/src/mklev.c
+++ b/src/mklev.c
@@ -1184,8 +1184,8 @@ themerooms_post_level_generate(void)
     iflags.in_lua = gi.in_mk_themerooms = FALSE;
 
     wallification(1, 0, COLNO - 1, ROWNO - 1);
-    free(gc.coder);
-    gc.coder = NULL;
+    if (gc.coder)
+        free(gc.coder), gc.coder = NULL;
     lua_gc(themes, LUA_GCCOLLECT);
 }