diff --git a/src/bin/pg_checksums/pg_checksums.c b/src/bin/pg_checksums/pg_checksums.c
index 7c7a75cdcd..b8e7c32dba 100644
--- a/src/bin/pg_checksums/pg_checksums.c
+++ b/src/bin/pg_checksums/pg_checksums.c
@@ -475,7 +475,7 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
-	/* Check if cluster is running */
+	/* Read the control file and check compatibility */
 	ControlFile = get_controlfile(DataDir, &crc_ok);
 	if (!crc_ok)
 	{
@@ -497,6 +497,11 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
+	/*
+	 * Check if cluster is running.  A clean shutdown is required to avoid
+	 * random checksum failures caused by torn pages.  Note that this doesn't
+	 * guard against someone starting the cluster concurrently.
+	 */
 	if (ControlFile->state != DB_SHUTDOWNED &&
 		ControlFile->state != DB_SHUTDOWNED_IN_RECOVERY)
 	{