diff --git a/Python/_warnings.c b/Python/_warnings.c
index 99f6071..615a2d3 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -517,7 +517,7 @@
     }
     else {
         const char *module_str = _PyUnicode_AsString(*module);
-        Py_XDECREF(*filename);
+        *filename = NULL;
         if (module_str == NULL)
                 goto handle_error;
         if (strcmp(module_str, "__main__") == 0) {