diff --git a/layout/generic/nsBlockFrame.cpp b/layout/generic/nsBlockFrame.cpp
index 8539001f309e..87c6baaa9077 100644
--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -2731,12 +2731,12 @@ nsBlockFrame::PullFrameFrom(nsLineBox*           aLine,
 
 void
 nsBlockFrame::SlideLine(nsBlockReflowState& aState,
-                        nsLineBox* aLine, nscoord aDY)
+                        nsLineBox* aLine, nscoord aDeltaBCoord)
 {
-  NS_PRECONDITION(aDY != 0, "why slide a line nowhere?");
+  NS_PRECONDITION(aDeltaBCoord != 0, "why slide a line nowhere?");
 
   // Adjust line state
-  aLine->SlideBy(aDY, aState.mContainerWidth);
+  aLine->SlideBy(aDeltaBCoord, aState.mContainerWidth);
 
   // Adjust the frames in the line
   nsIFrame* kid = aLine->mFirstChild;
@@ -2744,23 +2744,27 @@ nsBlockFrame::SlideLine(nsBlockReflowState& aState,
     return;
   }
 
+  WritingMode wm = GetWritingMode();
+  nsPoint physicalDelta =
+    LogicalPoint(wm, 0, aDeltaBCoord).GetPhysicalPoint(wm, 0);
+
   if (aLine->IsBlock()) {
-    if (aDY) {
-      kid->MovePositionBy(nsPoint(0, aDY));
+    if (aDeltaBCoord) {
+      kid->MovePositionBy(physicalDelta);
     }
 
     // Make sure the frame's view and any child views are updated
     nsContainerFrame::PlaceFrameView(kid);
   }
   else {
-    // Adjust the Y coordinate of the frames in the line.
-    // Note: we need to re-position views even if aDY is 0, because
+    // Adjust the block-dir coordinate of the frames in the line.
+    // Note: we need to re-position views even if aDeltaBCoord is 0, because
     // one of our parent frames may have moved and so the view's position
-    // relative to its parent may have changed
+    // relative to its parent may have changed.
     int32_t n = aLine->GetChildCount();
     while (--n >= 0) {
-      if (aDY) {
-        kid->MovePositionBy(nsPoint(0, aDY));
+      if (aDeltaBCoord) {
+        kid->MovePositionBy(physicalDelta);
       }
       // Make sure the frame's view and any child views are updated
       nsContainerFrame::PlaceFrameView(kid);
diff --git a/layout/generic/nsBlockFrame.h b/layout/generic/nsBlockFrame.h
index 72b13783d9f0..f3c5b2d012bb 100644
--- a/layout/generic/nsBlockFrame.h
+++ b/layout/generic/nsBlockFrame.h
@@ -408,11 +408,11 @@ protected:
     mState |= aFlags;
   }
 
-  /** move the frames contained by aLine by aDY
+  /** move the frames contained by aLine by aDeltaBCoord
     * if aLine is a block, its child floats are added to the state manager
     */
   void SlideLine(nsBlockReflowState& aState,
-                 nsLineBox* aLine, nscoord aDY);
+                 nsLineBox* aLine, nscoord aDeltaBCoord);
 
   void ComputeFinalSize(const nsHTMLReflowState& aReflowState,
                         nsBlockReflowState&      aState,