diff --git a/src/backend/tcop/dest.c b/src/backend/tcop/dest.c
index c952cbea8b..e6934d7b66 100644
--- a/src/backend/tcop/dest.c
+++ b/src/backend/tcop/dest.c
@@ -179,12 +179,11 @@ EndCommand(const QueryCompletion *qc, CommandDest dest, bool force_undecorated_o
 			 * We assume the tagname is plain ASCII and therefore requires no
 			 * encoding conversion.
 			 *
-			 * We no longer display LastOid, but to preserve the wire
-			 * protocol, we write InvalidOid where the LastOid used to be
-			 * written.
-			 *
-			 * All cases where LastOid was written also write nprocessed
-			 * count, so just Assert that rather than having an extra test.
+			 * In ancient versions of PostgreSQL, INSERT used to include the
+			 * Oid of the inserted record in the completion tag.  We no longer
+			 * support tables with Oids, so to maintain compatibility in the
+			 * wire protocol, we write a "0" for InvalidOid in the location
+			 * where we once wrote the inserted record's Oid.
 			 */
 			tag = qc->commandTag;
 			tagname = GetCommandTagName(tag);