diff --git a/src/OpenTK/Platform/Windows/WinGLNative.cs b/src/OpenTK/Platform/Windows/WinGLNative.cs
index f486d896..ef437d3c 100644
--- a/src/OpenTK/Platform/Windows/WinGLNative.cs
+++ b/src/OpenTK/Platform/Windows/WinGLNative.cs
@@ -747,11 +747,11 @@ namespace OpenTK.Platform.Windows
 
                 case WindowMessage.MOUSEWHEEL:
                     HandleMouseWheel(handle, message, wParam, lParam);
-                    break;
+                    return IntPtr.Zero;
 
                 case WindowMessage.MOUSEHWHEEL:
                     HandleMouseHWheel(handle, message, wParam, lParam);
-                    break;
+                    return IntPtr.Zero;
 
                 case WindowMessage.LBUTTONDOWN:
                     HandleLButtonDown(handle, message, wParam, lParam);