diff --git a/bots/check-mirroring b/bots/check-mirroring
index 143e25a..ea00a2a 100755
--- a/bots/check-mirroring
+++ b/bots/check-mirroring
@@ -111,7 +111,7 @@ def send_zephyr(zwrite_args, content, retry=False):
                          stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     stdout, stderr = p.communicate(input=content.encode("utf-8"))
     if p.returncode != 0:
-        if not retry and "Detected server failure while receiving acknowledgement for" in stderr:
+        if not retry and "Detected server failure while receiving acknowledgement for" in stdout:
             logger.warning("Got server failure error sending zephyr; retrying")
             logger.warning(stderr)
             # Retry sending the message rather than bailing.