diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 2a99c1f..71c6ae2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -2816,23 +2816,23 @@ WaitForStandbyConfirmation(XLogRecPtr wait_for_lsn)
 static void
 RaiseSlotInvalidationError(ReplicationSlot *slot)
 {
-	StringInfoData err_detail;
+	StringInfo err_detail = makeStringInfo();
 
-	initStringInfo(&err_detail);
+	Assert(slot->data.invalidated != RS_INVAL_NONE);
 
 	switch (slot->data.invalidated)
 	{
 		case RS_INVAL_WAL_REMOVED:
-			appendStringInfo(&err_detail, _("This slot has been invalidated because the required WAL has been removed."));
+			appendStringInfoString(err_detail, _("This slot has been invalidated because the required WAL has been removed."));
 			break;
 
 		case RS_INVAL_HORIZON:
-			appendStringInfo(&err_detail, _("This slot has been invalidated because the required rows have been removed."));
+			appendStringInfoString(err_detail, _("This slot has been invalidated because the required rows have been removed."));
 			break;
 
 		case RS_INVAL_WAL_LEVEL:
 			/* translator: %s is a GUC variable name */
-			appendStringInfo(&err_detail, _("This slot has been invalidated because \"%s\" is insufficient for slot."),
+			appendStringInfo(err_detail, _("This slot has been invalidated because \"%s\" is insufficient for slot."),
 							 "wal_level");
 			break;
 
@@ -2844,5 +2844,5 @@ RaiseSlotInvalidationError(ReplicationSlot *slot)
 			errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 			errmsg("can no longer get changes from replication slot \"%s\"",
 				   NameStr(slot->data.name)),
-			errdetail_internal("%s", err_detail.data));
+			errdetail_internal("%s", err_detail->data));
 }