diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 536b855531b7..995db67be6c0 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -1302,7 +1302,11 @@ gfx3DMatrix
 nsLayoutUtils::GetTransformToAncestor(nsIFrame *aFrame, const nsIFrame *aAncestor)
 {
   nsIFrame* parent;
-  gfx3DMatrix ctm = aFrame->GetTransformMatrix(aAncestor, &parent);
+  gfx3DMatrix ctm;
+  if (aFrame == aAncestor) {
+    return ctm;
+  }
+  ctm = aFrame->GetTransformMatrix(aAncestor, &parent);
   while (parent && parent != aAncestor) {
     if (!parent->Preserves3DChildren()) {
       ctm.ProjectTo2D();
diff --git a/layout/generic/test/test_bug791616.html b/layout/generic/test/test_bug791616.html
index 38b4de30adcb..4fd2b1e0975b 100644
--- a/layout/generic/test/test_bug791616.html
+++ b/layout/generic/test/test_bug791616.html
@@ -35,7 +35,9 @@ t.scrollTop = 0;
 var targetY = target.getBoundingClientRect().top;
 
 SimpleTest.waitForFocus(function() {
+  is(target.getBoundingClientRect().top, targetY, "Target should not have scrolled due to waitForFocus");
   t.focus();
+  is(target.getBoundingClientRect().top, targetY, "Target should not have scrolled due to focus change");
 
   // Move the caret to scroll it into view
   sel.collapse(target.firstChild, 2);