--- a/layout/painting/RetainedDisplayListBuilder.cpp
+++ b/layout/painting/RetainedDisplayListBuilder.cpp
@@ -1104,17 +1104,25 @@ RetainedDisplayListBuilder::AttemptParti
   // nsLayoutUtils::InvalidateForDisplayPortChange. The display port change also
   // marks the frame modified, so those regions are cleared here as well.
   AutoClearFramePropsArray modifiedFrames;
   AutoClearFramePropsArray framesWithProps;
   GetModifiedAndFramesWithProps(&mBuilder, &modifiedFrames.Frames(), &framesWithProps.Frames());
 
   // Do not allow partial builds if the retained display list is empty, or if
   // ShouldBuildPartial heuristic fails.
-  const bool shouldBuildPartial = !mList.IsEmpty() && ShouldBuildPartial(modifiedFrames.Frames());
+  bool shouldBuildPartial = !mList.IsEmpty() && ShouldBuildPartial(modifiedFrames.Frames());
+
+  // We don't support retaining with overlay scrollbars, since they require
+  // us to look at the display list and pick the highest z-index, which
+  // we can't do during partial building.
+  if (mBuilder.BuiltOverlayScrollbars()) {
+    shouldBuildPartial = false;
+    mBuilder.SetBuiltOverlayScrollbars(false);
+  }
 
   if (mPreviousCaret != mBuilder.GetCaretFrame()) {
     if (mPreviousCaret) {
       if (mBuilder.MarkFrameModifiedDuringBuilding(mPreviousCaret)) {
         modifiedFrames.Frames().AppendElement(mPreviousCaret);
       }
     }