diff --git a/src/backend/utils/adt/acl.c b/src/backend/utils/adt/acl.c
index d5285e2..3b963a0 100644
--- a/src/backend/utils/adt/acl.c
+++ b/src/backend/utils/adt/acl.c
@@ -2837,10 +2837,20 @@ convert_column_name(Oid tableoid, text *column)
 	colname = text_to_cstring(column);
 	attnum = get_attnum(tableoid, colname);
 	if (attnum == InvalidAttrNumber)
+	{
+		char	   *tablename = get_rel_name(tableoid);
+
+		/* Paranoia is necessary since tableoid could be anything */
+		if (tablename == NULL)
+			ereport(ERROR,
+					(errcode(ERRCODE_UNDEFINED_TABLE),
+					 errmsg("relation with OID %u does not exist",
+							tableoid)));
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_COLUMN),
 				 errmsg("column \"%s\" of relation \"%s\" does not exist",
-						colname, get_rel_name(tableoid))));
+						colname, tablename)));
+	}
 	pfree(colname);
 	return attnum;
 }