diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 2fa045e6b0f..8d2b0f1193d 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -225,7 +225,9 @@ CreateSharedMemoryAndSemaphores(void)
 	InitShmemAccess(seghdr);
 
 	/*
-	 * Create semaphores
+	 * Create semaphores.  (This is done here for historical reasons.  We used
+	 * to support emulating spinlocks with semaphores, which required
+	 * initializing semaphores early.)
 	 */
 	PGReserveSemaphores(numSemas);