diff --git a/when/when.d.ts b/when/when.d.ts
index ca2400fc5..60d569a17 100644
--- a/when/when.d.ts
+++ b/when/when.d.ts
@@ -61,8 +61,8 @@ declare module When {
         catch<U>(exceptionType: any, onRejected?: (reason: any) => Promise<U>): Promise<U>;
         catch<U>(exceptionType: any, onRejected?: (reason: any) => U): Promise<U>;
 
-        catch<U>(filter: (reason: any) => Boolean, onRejected?: (reason: any) => Promise<U>): Promise<U>;
-        catch<U>(filter: (reason: any) => Boolean, onRejected?: (reason: any) => U): Promise<U>;
+        catch<U>(filter: (reason: any) => boolean, onRejected?: (reason: any) => Promise<U>): Promise<U>;
+        catch<U>(filter: (reason: any) => boolean, onRejected?: (reason: any) => U): Promise<U>;
 
         catch<U>(onRejected?: (reason: any) => Promise<U>): Promise<U>;
         catch<U>(onRejected?: (reason: any) => U): Promise<U>;