diff --git a/rest/rest-tests.ts b/rest/rest-tests.ts
index f291e53c0..905084318 100644
--- a/rest/rest-tests.ts
+++ b/rest/rest-tests.ts
@@ -91,12 +91,18 @@ interface KnownConfig {
     prop: string;
 }
 var knownConfig = interceptor({
-    init: (config: KnownConfig) => {
-        config.prop = config.prop || 'default-value';
-        return config;
-    },
     success: (response: rest.Response, config: KnownConfig) => {
-        console.log(config.prop);
+        console.log(config);
+        return response;
+    },
+});
+
+var transformedConfig = interceptor({
+    init: (config: KnownConfig) => {
+        return config.prop;
+    },
+    success: (response: rest.Response, config: string) => {
+        console.log(config);
         return response;
     },
 });
@@ -127,4 +133,5 @@ client = rest
     .wrap(xhr)
     .wrap(noop)
     .wrap(fail)
-    .wrap(knownConfig, { prop: 'value' });
+    .wrap(knownConfig, { prop: 'value' })
+    .wrap(transformedConfig, { prop: 'value' });
diff --git a/rest/rest.d.ts b/rest/rest.d.ts
index 98c214537..ef7fc2abf 100644
--- a/rest/rest.d.ts
+++ b/rest/rest.d.ts
@@ -71,15 +71,15 @@ declare module "rest/interceptor" {
 	import when = require("when");
 	import rest = require("rest");
 
-	function interceptor<T>(config: interceptor.Config<T>): rest.Interceptor<T>;
+	function interceptor<T, U>(config: interceptor.Config<T, U>): rest.Interceptor<T>;
 
 	module interceptor {
-		interface Config<T> {
-			init?: (config: T) => T;
-			request?: (request: rest.Request, config: T, meta: rest.Meta) => rest.Request | when.Promise<rest.Request>;
-			response?: (response: rest.Response, config: T, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
-			success?: (response: rest.Response, config: T, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
-			error?: (response: rest.Response, config: T, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
+		interface Config<T, U> {
+			init?: (config: T) => U;
+			request?: (request: rest.Request, config: U, meta: rest.Meta) => rest.Request | when.Promise<rest.Request>;
+			response?: (response: rest.Response, config: U, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
+			success?: (response: rest.Response, config: U, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
+			error?: (response: rest.Response, config: U, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
 		}
 	}