diff --git a/cli/compose/schema/data/config_schema_v3.9.json b/cli/compose/schema/data/config_schema_v3.9.json
index c6f63fda46d3..0ee21c1b7936 100644
--- a/cli/compose/schema/data/config_schema_v3.9.json
+++ b/cli/compose/schema/data/config_schema_v3.9.json
@@ -91,7 +91,8 @@
                 "shm_size": {"type": ["integer", "string"]},
                 "extra_hosts": {"$ref": "#/definitions/list_or_dict"}
               },
-              "additionalProperties": false
+              "additionalProperties": false,
+              "patternProperties": {"^x-": {}}
             }
           ]
         },