diff --git a/Python/ast.c b/Python/ast.c
index b9beef8..d1aa616 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -131,7 +131,12 @@
         Py_INCREF(Py_None);
         loc = Py_None;
     }
-    filename_obj = PyUnicode_DecodeFSDefault(filename);
+    if (filename != NULL)
+        filename_obj = PyUnicode_DecodeFSDefault(filename);
+    else {
+        Py_INCREF(Py_None);
+        filename_obj = Py_None;
+    }
     if (filename_obj != NULL)
         tmp = Py_BuildValue("(NlOO)", filename_obj, lineno, offset, loc);
     else