diff --git a/gfx/layers/apz/src/AsyncPanZoomController.cpp b/gfx/layers/apz/src/AsyncPanZoomController.cpp
index 0bbe763793a6..3b04e7e2a0be 100644
--- a/gfx/layers/apz/src/AsyncPanZoomController.cpp
+++ b/gfx/layers/apz/src/AsyncPanZoomController.cpp
@@ -1828,8 +1828,16 @@ nsEventStatus AsyncPanZoomController::OnPan(const PanGestureInput& aEvent, bool
       *CurrentPanGestureBlock()->GetOverscrollHandoffChain(),
       panDistance,
       ScrollSource::Wheel);
+
+  // Create fake "touch" positions that will result in the desired scroll motion.
+  // Note that the pan displacement describes the change in scroll position:
+  // positive displacement values mean that the scroll position increases.
+  // However, an increase in scroll position means that the scrolled contents
+  // are moved to the left / upwards. Since our simulated "touches" determine
+  // the motion of the scrolled contents, not of the scroll position, they need
+  // to move in the opposite direction of the pan displacement.
   ParentLayerPoint startPoint = aEvent.mLocalPanStartPoint;
-  ParentLayerPoint endPoint = aEvent.mLocalPanStartPoint + aEvent.mLocalPanDisplacement;
+  ParentLayerPoint endPoint = aEvent.mLocalPanStartPoint - aEvent.mLocalPanDisplacement;
   CallDispatchScroll(startPoint, endPoint, handoffState);
 
   return nsEventStatus_eConsumeNoDefault;
diff --git a/gfx/layers/apz/src/Axis.cpp b/gfx/layers/apz/src/Axis.cpp
index 1684016125d4..5a38852dc4b5 100644
--- a/gfx/layers/apz/src/Axis.cpp
+++ b/gfx/layers/apz/src/Axis.cpp
@@ -76,7 +76,7 @@ void Axis::UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos, ParentLayerCoord
     return;
   }
 
-  float newVelocity = mAxisLocked ? 0.0f : (float)(mPos - aPos + aAdditionalDelta) / (float)(aTimestampMs - mPosTimeMs);
+  float newVelocity = mAxisLocked ? 0.0f : (float)(mPos - aPos - aAdditionalDelta) / (float)(aTimestampMs - mPosTimeMs);
   if (gfxPrefs::APZMaxVelocity() > 0.0f) {
     bool velocityIsNegative = (newVelocity < 0);
     newVelocity = fabs(newVelocity);
diff --git a/gfx/layers/apz/src/Axis.h b/gfx/layers/apz/src/Axis.h
index 2294510f7b36..1da9dcf3e42c 100644
--- a/gfx/layers/apz/src/Axis.h
+++ b/gfx/layers/apz/src/Axis.h
@@ -43,6 +43,9 @@ public:
   /**
    * Notify this Axis that a new touch has been received, including a timestamp
    * for when the touch was received. This triggers a recalculation of velocity.
+   * This can also used for pan gesture events. For those events, the "touch"
+   * location is stationary and the scroll displacement is passed in as
+   * aAdditionalDelta.
    */
   void UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos, ParentLayerCoord aAdditionalDelta, uint32_t aTimestampMs);
 
diff --git a/layout/base/UnitTransforms.h b/layout/base/UnitTransforms.h
index 6d162f307fac..c952c839e590 100644
--- a/layout/base/UnitTransforms.h
+++ b/layout/base/UnitTransforms.h
@@ -217,7 +217,7 @@ static Maybe<gfx::PointTyped<TargetUnits>> UntransformVector(const gfx::Matrix4x
   if (!projectedAnchor.HasPositiveWCoord() || !projectedTarget.HasPositiveWCoord()){
     return Nothing();
   }
-  return Some(ViewAs<TargetUnits>(projectedAnchor.As2DPoint() - projectedTarget.As2DPoint()));
+  return Some(ViewAs<TargetUnits>(projectedTarget.As2DPoint() - projectedAnchor.As2DPoint()));
 }
 
 } // namespace mozilla