diff --git a/types/p2/index.d.ts b/types/p2/index.d.ts
index 95082f836d..7a3715c7c7 100644
--- a/types/p2/index.d.ts
+++ b/types/p2/index.d.ts
@@ -431,7 +431,7 @@ declare namespace p2 {
 
     export class EventEmitter {
 
-        on(type: string, listener: Function, context: any): EventEmitter;
+        on(type: string, listener: Function, context?: any): EventEmitter;
         has(type: string, listener: Function): boolean;
         off(type: string, listener: Function): EventEmitter;
         emit(event: any): EventEmitter;