diff --git a/libs/hackbot-runtime/hackbot_runtime/actions/phabricator.py b/libs/hackbot-runtime/hackbot_runtime/actions/phabricator.py
index a760b2f6a6..1f6f565877 100644
--- a/libs/hackbot-runtime/hackbot_runtime/actions/phabricator.py
+++ b/libs/hackbot-runtime/hackbot_runtime/actions/phabricator.py
@@ -58,7 +58,9 @@ async def submit_patch(
         Field(
             description=(
                 "Title for the new revision: a single line describing the fix, "
-                "as you would write a commit message subject."
+                "as you would write a commit message subject. Do not include "
+                "reviewer annotations (r=... or r?...): reviewer selection is "
+                "handled on the Phabricator side."
             )
         ),
     ],