--- a/gfx/layers/apz/src/AndroidAPZ.cpp
+++ b/gfx/layers/apz/src/AndroidAPZ.cpp
@@ -132,17 +132,17 @@ AndroidFlingAnimation::DoSample(FrameMet
   ParentLayerPoint velocity = mPreviousVelocity;
 
   // Sometimes the OverScroller fails to update the offset for a frame.
   // If the frame can still scroll we just use the velocity from the previous
   // frame. However, if the frame can no longer scroll in the direction
   // of the fling, then end the animation.
   if (offset != mPreviousOffset) {
     if (aDelta.ToMilliseconds() > 0) {
-      velocity = (mPreviousOffset - offset) / (float)aDelta.ToMilliseconds();
+      velocity = (offset - mPreviousOffset) / (float)aDelta.ToMilliseconds();
       mPreviousVelocity = velocity;
     }
   } else if (hitBoundX || hitBoundY) {
     // We have reached the end of the scroll in one of the directions being scrolled and the offset has not
     // changed so end animation.
     shouldContinueFling = false;
   }