diff --git a/Source/OpenTK/Platform/MacOS/CocoaNativeWindow.cs b/Source/OpenTK/Platform/MacOS/CocoaNativeWindow.cs
index 001634f0..d187f1aa 100644
--- a/Source/OpenTK/Platform/MacOS/CocoaNativeWindow.cs
+++ b/Source/OpenTK/Platform/MacOS/CocoaNativeWindow.cs
@@ -540,7 +540,10 @@ namespace OpenTK.Platform.MacOS
                             // Only raise wheel events when the user has actually scrolled
                             if (dx != 0 || dy != 0)
                             {
-                                OnMouseWheel(dx, dy);
+                                // Note: OpenTK follows the win32 convention, where
+                                // (+h, +v) = (right, up). MacOS reports (+h, +v) = (left, up)
+                                // so we need to flip the horizontal scroll direction.
+                                OnMouseWheel(-dx, dy);
                             }
                         }
                         break;
diff --git a/Source/OpenTK/Platform/MacOS/HIDInput.cs b/Source/OpenTK/Platform/MacOS/HIDInput.cs
index 2483fde5..d13fdd32 100755
--- a/Source/OpenTK/Platform/MacOS/HIDInput.cs
+++ b/Source/OpenTK/Platform/MacOS/HIDInput.cs
@@ -180,9 +180,14 @@ namespace OpenTK.Platform.MacOS
                     break;
 
                 case CGEventType.ScrollWheel:
-                    CursorState.SetScrollRelative(
-                        (float)CG.EventGetDoubleValueField(@event, CGEventField.ScrollWheelEventPointDeltaAxis2) * MacOSFactory.ScrollFactor,
-                        (float)CG.EventGetDoubleValueField(@event, CGEventField.ScrollWheelEventPointDeltaAxis1) * MacOSFactory.ScrollFactor);
+                    {
+                        // Note: OpenTK follows the win32 convention, where
+                        // (+h, +v) = (right, up). MacOS reports (+h, +v) = (left, up)
+                        // so we need to flip the horizontal scroll direction.
+                        double h = CG.EventGetDoubleValueField(@event, CGEventField.ScrollWheelEventPointDeltaAxis2) * MacOSFactory.ScrollFactor;
+                        double v = CG.EventGetDoubleValueField(@event, CGEventField.ScrollWheelEventPointDeltaAxis1) * MacOSFactory.ScrollFactor;
+                        CursorState.SetScrollRelative((float)(-h), (float)v);
+                    }
                     break;
 
                 case CGEventType.LeftMouseDown:
@@ -190,6 +195,7 @@ namespace OpenTK.Platform.MacOS
                 case CGEventType.OtherMouseDown:
                     {
                         int n = CG.EventGetIntegerValueField(@event, CGEventField.MouseEventButtonNumber);
+                        n = n == 1 ? 2 : n == 2 ? 1 : n; // flip middle and right button numbers to match OpenTK
                         MouseButton b = MouseButton.Left + n;
                         CursorState[b] = true;
                     }
@@ -200,6 +206,7 @@ namespace OpenTK.Platform.MacOS
                 case CGEventType.OtherMouseUp:
                     {
                         int n = CG.EventGetIntegerValueField(@event, CGEventField.MouseEventButtonNumber);
+                        n = n == 1 ? 2 : n == 2 ? 1 : n; // flip middle and right button numbers to match OpenTK
                         MouseButton b = MouseButton.Left + n;
                         CursorState[b] = false;
                     }