diff --git a/d3/d3.d.ts b/d3/d3.d.ts
index b3a365cdfe..aa6d299965 100644
--- a/d3/d3.d.ts
+++ b/d3/d3.d.ts
@@ -824,7 +824,7 @@ declare module d3 {
         attr(name: string, value: (datum: Datum, index: number) => Primitive): Transition<Datum>;
         attr(obj: { [key: string]: Primitive | ((datum: Datum, index: number) => Primitive) }): Transition<Datum>;
 
-        attrTween(name: string, tween: (datum: Datum, index: number, attr: string) => Primitive): Transition<Datum>;
+        attrTween(name: string, tween: (datum: Datum, index: number, attr: string) => (t: number) => Primitive): Transition<Datum>;
 
         style(name: string, value: Primitive, priority?: string): Transition<Datum>;
         style(name: string, value: (datum: Datum, index: number) => Primitive, priority?: string): Transition<Datum>;