diff --git a/interfaces.d.ts b/interfaces.d.ts
index 4fdbeb40b1..41579bdb33 100644
--- a/interfaces.d.ts
+++ b/interfaces.d.ts
@@ -29,7 +29,7 @@ export interface PolymerInit {
   _template?: HTMLTemplateElement;
   hostAttributes?: {[key: string]: any};
   listeners?: {[key: string]: string};
-  behaviors?: PolymerInit | PolymerInit[];
+  behaviors?: BehaviorInit | BehaviorInit[];
 
   // Lifecycle methods
   registered?(): void;
@@ -43,6 +43,11 @@ export interface PolymerInit {
   [others: string]: any;
 }
 
+export type BehaviorInit = Pick<
+  PolymerInit,
+  Exclude<keyof PolymerInit, "is" | "extends" | "_template">
+>;
+
 // Types from "externs/polymer-internal-shared-types.js"
 
 export interface StampedTemplate extends DocumentFragment {