diff --git a/draft-06/schema b/draft-06/schema
index 621cc510..5c414473 100644
--- a/draft-06/schema
+++ b/draft-06/schema
@@ -110,6 +110,7 @@
         },
         "patternProperties": {
             "type": "object",
+            "propertyNames": { "format": "regex" },
             "additionalProperties": { "$ref": "#" },
             "default": {}
         },