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..8f303040 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;
                     }
@@ -406,6 +413,11 @@ namespace OpenTK.Platform.MacOS
                             mouse.State.Y += v_int;
                             break;
 
+                        case HIDUsageGD.Z:
+                            // Horizontal scrolling for apple mouse (old-style with trackball)
+                            mouse.State.SetScrollRelative(v_int, 0);
+                            break;
+
                         case HIDUsageGD.Wheel:
                             mouse.State.SetScrollRelative(0, v_int);
                             break;
diff --git a/Source/OpenTK/Platform/MacOS/MacOSFactory.cs b/Source/OpenTK/Platform/MacOS/MacOSFactory.cs
index 9c79119b..43e7bd75 100644
--- a/Source/OpenTK/Platform/MacOS/MacOSFactory.cs
+++ b/Source/OpenTK/Platform/MacOS/MacOSFactory.cs
@@ -37,6 +37,9 @@ namespace OpenTK.Platform.MacOS
 
     class MacOSFactory : PlatformFactoryBase
     {
+        // Todo: we can query the exact amount via
+        // CGEventSourceGetPixelsPerLine. This is
+        // approximately 0.1f
         internal const float ScrollFactor = 0.1f;
         internal static bool ExclusiveFullscreen = false;
 
diff --git a/Source/OpenTK/Platform/X11/XI2MouseKeyboard.cs b/Source/OpenTK/Platform/X11/XI2MouseKeyboard.cs
index 1ef31796..0df840ce 100644
--- a/Source/OpenTK/Platform/X11/XI2MouseKeyboard.cs
+++ b/Source/OpenTK/Platform/X11/XI2MouseKeyboard.cs
@@ -544,7 +544,11 @@ namespace OpenTK.Platform.X11
 
             d.State.X += (int)Math.Round(x);
             d.State.Y += (int)Math.Round(y);
-            d.State.SetScrollRelative((float)h, (float)v);
+
+            // Note: OpenTK follows the windows scrolling convention where
+            // (+h, +v) = (right, up). XI2 uses (+h, +v) = (right, down)
+            // instead, so we need to flip the vertical offset.
+            d.State.SetScrollRelative((float)h, (float)(-v));
         }
 
         unsafe static double ReadRawValue(ref XIRawEvent raw, int bit)