diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 064b847..152210b 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -1891,6 +1891,7 @@
         if (PyBytes_Check(result)) {
             PyErr_SetString(PyExc_TypeError,
                 "sum() can't sum bytes [use b''.join(seq) instead]");
+            Py_DECREF(iter);
             return NULL;
         }
         if (PyByteArray_Check(result)) {