diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index b8a88e61d4..8c7dbd2e0b 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -531,6 +531,11 @@ _asyncio_Future_remove_done_callback(FutureObj *self, PyObject *fn)
         if ((ret = PyObject_RichCompareBool(fn, item, Py_EQ)) < 0) {
             goto fail;
         }
+        if (j >= len) {
+            PyErr_SetString(PyExc_RuntimeError,
+                "Done callbacks modified while iterating.");
+            goto fail;
+        }
         if (ret == 0) {
             Py_INCREF(item);
             PyList_SET_ITEM(newlist, j, item);