diff --git a/python/message.c b/python/message.c
index 8d91b0f..327eb2e 100644
--- a/python/message.c
+++ b/python/message.c
@@ -1329,6 +1329,9 @@
     int err = PyBytes_AsStringAndSize(bytes, &buf, &size);
     (void)err;
     assert(err >= 0);
+  } else if (PyByteArray_Check(arg)) {
+    buf = PyByteArray_AS_STRING(arg);
+    size = PyByteArray_GET_SIZE(arg);
   } else if (PyBytes_AsStringAndSize(arg, &buf, &size) < 0) {
     return NULL;
   }