diff --git a/layout/tables/nsTableRowFrame.cpp b/layout/tables/nsTableRowFrame.cpp
index 929c59d2eeec..c83492085a55 100644
--- a/layout/tables/nsTableRowFrame.cpp
+++ b/layout/tables/nsTableRowFrame.cpp
@@ -164,6 +164,9 @@ nsTableRowFrame::Init(nsIContent*      aContent,
   // Let the base class do its initialization
   rv = nsHTMLContainerFrame::Init(aContent, aParent, aPrevInFlow);
 
+  NS_ASSERTION(NS_STYLE_DISPLAY_TABLE_ROW == GetStyleDisplay()->mDisplay,
+               "wrong display on table row frame");
+
   if (aPrevInFlow) {
     // Set the row index
     nsTableRowFrame* rowFrame = (nsTableRowFrame*)aPrevInFlow;
diff --git a/layout/tables/nsTableRowGroupFrame.cpp b/layout/tables/nsTableRowGroupFrame.cpp
index 0797247be095..15287087d9bb 100644
--- a/layout/tables/nsTableRowGroupFrame.cpp
+++ b/layout/tables/nsTableRowGroupFrame.cpp
@@ -1413,6 +1413,9 @@ nsTableRowGroupFrame::AppendFrames(nsIAtom*        aListName,
   for (nsIFrame* rowFrame = aFrameList; rowFrame;
        rowFrame = rowFrame->GetNextSibling()) {
     if (nsGkAtoms::tableRowFrame == rowFrame->GetType()) {
+      NS_ASSERTION(NS_STYLE_DISPLAY_TABLE_ROW ==
+                     rowFrame->GetStyleDisplay()->mDisplay,
+                   "wrong display type on rowframe");      
       rows.AppendElement(rowFrame);
     }
   }
@@ -1456,6 +1459,9 @@ nsTableRowGroupFrame::InsertFrames(nsIAtom*        aListName,
   for (nsIFrame* rowFrame = aFrameList; rowFrame;
        rowFrame = rowFrame->GetNextSibling()) {
     if (nsGkAtoms::tableRowFrame == rowFrame->GetType()) {
+      NS_ASSERTION(NS_STYLE_DISPLAY_TABLE_ROW ==
+                     rowFrame->GetStyleDisplay()->mDisplay,
+                   "wrong display type on rowframe");      
       rows.AppendElement(rowFrame);
       if (!gotFirstRow) {
         ((nsTableRowFrame*)rowFrame)->SetFirstInserted(PR_TRUE);