diff --git a/layout/generic/nsBlockFrame.cpp b/layout/generic/nsBlockFrame.cpp
index c5172d046354..497f535ca9ed 100644
--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -5013,7 +5013,7 @@ bool nsBlockFrame::DrainOverflowLines() {
       mLines.splice(mLines.begin(), overflowLines->mLines);
       NS_ASSERTION(overflowLines->mLines.empty(), "splice should empty list");
       delete overflowLines;
-      AddFrames(ocContinuations, mFrames.LastChild());
+      AddFrames(ocContinuations, mFrames.LastChild(), nullptr);
       didFindOverflow = true;
     }
   }
@@ -5339,7 +5339,7 @@ void nsBlockFrame::AppendFrames(ChildListID aListID, nsFrameList& aFrameList) {
     GetParent()->AddStateBits(NS_STATE_SVG_TEXT_CORRESPONDENCE_DIRTY);
   }
 
-  AddFrames(aFrameList, lastKid);
+  AddFrames(aFrameList, lastKid, nullptr);
   if (aListID != kNoReflowPrincipalList) {
     PresShell()->FrameNeedsReflow(
         this, IntrinsicDirty::TreeChange,
@@ -5375,7 +5375,7 @@ void nsBlockFrame::InsertFrames(ChildListID aListID, nsIFrame* aPrevFrame,
   printf("\n");
 #endif
 
-  AddFrames(aFrameList, aPrevFrame);
+  AddFrames(aFrameList, aPrevFrame, aPrevFrameLine);
   if (aListID != kNoReflowPrincipalList) {
     PresShell()->FrameNeedsReflow(
         this, IntrinsicDirty::TreeChange,
@@ -5436,7 +5436,8 @@ static bool ShouldPutNextSiblingOnNewLine(nsIFrame* aLastFrame) {
   return false;
 }
 
-void nsBlockFrame::AddFrames(nsFrameList& aFrameList, nsIFrame* aPrevSibling) {
+void nsBlockFrame::AddFrames(nsFrameList& aFrameList, nsIFrame* aPrevSibling,
+                             const nsLineList::iterator* aPrevSiblingLine) {
   // Clear our line cursor, since our lines may change.
   ClearLineCursor();
 
@@ -7027,7 +7028,7 @@ void nsBlockFrame::SetInitialChildList(ChildListID aListID,
                  "NS_BLOCK_HAS_FIRST_LETTER_STYLE state out of sync");
 #endif
 
-    AddFrames(aChildList, nullptr);
+    AddFrames(aChildList, nullptr, nullptr);
   } else {
     nsContainerFrame::SetInitialChildList(aListID, aChildList);
   }
diff --git a/layout/generic/nsBlockFrame.h b/layout/generic/nsBlockFrame.h
index 6511fd018d2c..2c53666196ad 100644
--- a/layout/generic/nsBlockFrame.h
+++ b/layout/generic/nsBlockFrame.h
@@ -485,8 +485,12 @@ class nsBlockFrame : public nsContainerFrame {
    * contains aPrevSibling and add aFrameList after aPrevSibling on that line.
    * New lines are created as necessary to handle block data in aFrameList.
    * This function will clear aFrameList.
+   *
+   * aPrevSiblingLine, if present, must be the line containing aPrevSibling.
+   * Providing it will make this function faster.
    */
-  void AddFrames(nsFrameList& aFrameList, nsIFrame* aPrevSibling);
+  void AddFrames(nsFrameList& aFrameList, nsIFrame* aPrevSibling,
+                 const nsLineList::iterator* aPrevSiblingLine);
 
   /**
    * Perform Bidi resolution on this frame