diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 2e6f7f4852..2ae231fd90 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -366,7 +366,7 @@ CREATE FUNCTION postgres_fdw_abs(int) RETURNS int AS $$
 BEGIN
 RETURN abs($1);
 END
-$$ LANGUAGE plpgsql IMMUTABLE;
+$$ LANGUAGE plpgsql IMMUTABLE STRICT;
 CREATE OPERATOR === (
     LEFTARG = int,
     RIGHTARG = int,