diff --git a/age--1.1.1.sql b/age--1.1.1.sql
index 8a4c1a826..692e95603 100644
--- a/age--1.1.1.sql
+++ b/age--1.1.1.sql
@@ -3413,7 +3413,7 @@ AS 'MODULE_PATHNAME';
 CREATE FUNCTION ag_catalog.age_id(agtype)
 RETURNS agtype
 LANGUAGE c
-STABLE
+IMMUTABLE
 RETURNS NULL ON NULL INPUT
 PARALLEL SAFE
 AS 'MODULE_PATHNAME';
@@ -3421,7 +3421,7 @@ AS 'MODULE_PATHNAME';
 CREATE FUNCTION ag_catalog.age_start_id(agtype)
 RETURNS agtype
 LANGUAGE c
-STABLE
+IMMUTABLE
 RETURNS NULL ON NULL INPUT
 PARALLEL SAFE
 AS 'MODULE_PATHNAME';
@@ -3429,7 +3429,7 @@ AS 'MODULE_PATHNAME';
 CREATE FUNCTION ag_catalog.age_end_id(agtype)
 RETURNS agtype
 LANGUAGE c
-STABLE
+IMMUTABLE
 RETURNS NULL ON NULL INPUT
 PARALLEL SAFE
 AS 'MODULE_PATHNAME';