diff --git a/Python/ast.c b/Python/ast.c
index eb4c68b..be58f53 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -274,6 +274,8 @@
                 return Interactive(stmts, arena);
             }
         default:
+            PyErr_Format(PyExc_SystemError,
+                         "invalid node %d for PyAST_FromNode", TYPE(n));
             goto error;
     }
  error: