diff --git a/src/spectator/mocks/nil_method_stub.cr b/src/spectator/mocks/nil_method_stub.cr
index d8421c3..798d378 100644
--- a/src/spectator/mocks/nil_method_stub.cr
+++ b/src/spectator/mocks/nil_method_stub.cr
@@ -4,7 +4,7 @@ require "./value_method_stub"
 
 module Spectator::Mocks
   class NilMethodStub < GenericMethodStub(Nil)
-    def call(_args : GenericArguments(T, NT)) : ReturnType forall T, NT
+    def call(_args : GenericArguments(T, NT)) : Nil forall T, NT
       nil
     end