diff --git a/src/backend/catalog/objectaddress.c b/src/backend/catalog/objectaddress.c
index de2a26dada..ec4c98769a 100644
--- a/src/backend/catalog/objectaddress.c
+++ b/src/backend/catalog/objectaddress.c
@@ -116,7 +116,7 @@ static ObjectPropertyType ObjectProperty[] =
 		ExtensionRelationId,
 		ExtensionOidIndexId,
 		-1,
-		Anum_pg_extension_extnamespace
+		InvalidAttrNumber		/* extension doesn't belong to extnamespace */
 	},
 	{
 		ForeignDataWrapperRelationId,