diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 984c2861cc..d38164caa7 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -1929,6 +1929,8 @@ BackendXidGetPid(TransactionId xid)
 
 /*
  * IsBackendPid -- is a given pid a running backend
+ *
+ * This is not called by the backend, but is called by external modules.
  */
 bool
 IsBackendPid(int pid)