diff --git a/video/out/cocoa/view.m b/video/out/cocoa/view.m
index 2ae81abda9..e2891ffd3d 100644
--- a/video/out/cocoa/view.m
+++ b/video/out/cocoa/view.m
@@ -190,7 +190,7 @@
         [self.adapter putAxis:cmd delta:delta];
     } else {
         const int modifiers = [event modifierFlags];
-        const int mpkey = delta > 0 ? MP_MOUSE_BTN3 : MP_MOUSE_BTN4;
+        const int mpkey = [event deltaY] > 0 ? MP_MOUSE_BTN3 : MP_MOUSE_BTN4;
         [self.adapter putKey:mpkey withModifiers:modifiers];
     }
 }