diff --git a/ldclient-js/ldclient-js-tests.ts b/ldclient-js/ldclient-js-tests.ts
index 2e304187dd..cf4ec2b2b6 100644
--- a/ldclient-js/ldclient-js-tests.ts
+++ b/ldclient-js/ldclient-js-tests.ts
@@ -6,6 +6,9 @@ const ldClient = LDClient.initialize(
     {
         key: 'USER KEY',
         name: 'USER NAME',
+        custom: {
+            'CUSTOM ATTRIBUTE': ['CUSTOM VALUE'],
+        },
     },
     {
         hash: 'SECURE USER HASH',
diff --git a/ldclient-js/ldclient-js.d.ts b/ldclient-js/ldclient-js.d.ts
index 1a0ae97550..47792db29a 100644
--- a/ldclient-js/ldclient-js.d.ts
+++ b/ldclient-js/ldclient-js.d.ts
@@ -131,7 +131,9 @@ declare namespace LaunchDarkly {
         /**
          * Any additional attributes associated with the user.
          */
-        custom?: string | boolean | number | Array<string | boolean | number>;
+        custom?: {
+            [key: string]: string | boolean | number | Array<string | boolean | number>,
+        };
     }
 
     /**