diff --git a/mozilla/layout/generic/nsInlineFrame.cpp b/mozilla/layout/generic/nsInlineFrame.cpp
index 3ccf389839e..5ef4bd4310a 100644
--- a/mozilla/layout/generic/nsInlineFrame.cpp
+++ b/mozilla/layout/generic/nsInlineFrame.cpp
@@ -252,6 +252,10 @@ nsInlineFrame::ReparentFloatsForInlineChild(nsIFrame* aOurLineContainer,
   NS_ASSERTION(aOurLineContainer->GetNextContinuation() ||
                aOurLineContainer->GetPrevContinuation(),
                "Don't call this when we have no continuation, it's a waste");
+  if (!aFrame) {
+    NS_ASSERTION(aReparentSiblings, "Why did we get called?");
+    return;
+  }
 
   nsIFrame* ancestor = aFrame;
   nsIFrame* ancestorBlockChild;