diff --git a/src/backend/catalog/aclchk.c b/src/backend/catalog/aclchk.c
index bd006931938..02a754cc30a 100644
--- a/src/backend/catalog/aclchk.c
+++ b/src/backend/catalog/aclchk.c
@@ -3004,10 +3004,6 @@ pg_aclmask(ObjectType objtype, Oid object_oid, AttrNumber attnum, Oid roleid,
  * Exported routines for examining a user's privileges for various objects
  *
  * See aclmask() for a description of the common API for these functions.
- *
- * Note: we give lookup failure the full ereport treatment because the
- * has_xxx_privilege() family of functions allow users to pass any random
- * OID to these functions.
  * ****************************************************************
  */
 
@@ -3074,10 +3070,8 @@ object_aclmask_ext(Oid classid, Oid objectid, Oid roleid,
 			return 0;
 		}
 		else
-			ereport(ERROR,
-					(errcode(ERRCODE_UNDEFINED_OBJECT),
-					 errmsg("%s with OID %u does not exist",
-							get_object_class_descr(classid), objectid)));
+			elog(ERROR, "cache lookup failed for %s %u",
+				 get_object_class_descr(classid), objectid);
 	}
 
 	ownerId = DatumGetObjectId(SysCacheGetAttrNotNull(cacheid,
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index e560fef6919..011d8d4da5a 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -170,6 +170,15 @@ pg_database_size_oid(PG_FUNCTION_ARGS)
 	Oid			dbOid = PG_GETARG_OID(0);
 	int64		size;
 
+	/*
+	 * Not needed for correctness, but avoid non-user-facing error message
+	 * later if the database doesn't exist.
+	 */
+	if (!SearchSysCacheExists1(DATABASEOID, ObjectIdGetDatum(dbOid)))
+		ereport(ERROR,
+				errcode(ERRCODE_UNDEFINED_OBJECT),
+				errmsg("database with OID %u does not exist", dbOid));
+
 	size = calculate_database_size(dbOid);
 
 	if (size == 0)
@@ -274,6 +283,15 @@ pg_tablespace_size_oid(PG_FUNCTION_ARGS)
 	Oid			tblspcOid = PG_GETARG_OID(0);
 	int64		size;
 
+	/*
+	 * Not needed for correctness, but avoid non-user-facing error message
+	 * later if the tablespace doesn't exist.
+	 */
+	if (!SearchSysCacheExists1(TABLESPACEOID, ObjectIdGetDatum(tblspcOid)))
+		ereport(ERROR,
+				errcode(ERRCODE_UNDEFINED_OBJECT),
+				errmsg("tablespace with OID %u does not exist", tblspcOid));
+
 	size = calculate_tablespace_size(tblspcOid);
 
 	if (size < 0)