diff --git a/mozilla/layout/mathml/base/src/nsMathMLChar.cpp b/mozilla/layout/mathml/base/src/nsMathMLChar.cpp
index cc63c7de2f7..88796ab9555 100644
--- a/mozilla/layout/mathml/base/src/nsMathMLChar.cpp
+++ b/mozilla/layout/mathml/base/src/nsMathMLChar.cpp
@@ -1602,7 +1602,9 @@ nsMathMLChar::Stretch(nsPresContext*      aPresContext,
     targetSize = aContainerSize.width;
   }
   // if we are not a largeop in display mode, return if size fits
-  if (targetSize <= 0 || (!largeop && IsSizeOK(charSize, targetSize, aStretchHint))) {
+  if ((targetSize <= 0) || 
+      (!largeop && ((isVertical && charSize >= targetSize) ||
+                     IsSizeOK(charSize, targetSize, aStretchHint)))) {
     // ensure that the char later behaves like a normal char
     // (will be reset back to its intrinsic value in case of dynamic updates)
     mDirection = NS_STRETCH_DIRECTION_UNSUPPORTED;