diff --git a/layout/generic/nsBlockFrame.cpp b/layout/generic/nsBlockFrame.cpp
index b17dab65a501..2064c2b971b3 100644
--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -5188,6 +5188,7 @@ nsBlockInFlowLineIterator::Prev()
   PRBool currentlyInOverflowLines = mInOverflowLines != nsnull;
   while (PR_TRUE) {
     if (currentlyInOverflowLines) {
+      mInOverflowLines = nsnull;
       mLine = mFrame->end_lines();
       if (mLine != mFrame->begin_lines()) {
         --mLine;