diff --git a/mozilla/gfx/thebes/src/gfxFont.cpp b/mozilla/gfx/thebes/src/gfxFont.cpp
index a9928c82c92..606c5d24e09 100644
--- a/mozilla/gfx/thebes/src/gfxFont.cpp
+++ b/mozilla/gfx/thebes/src/gfxFont.cpp
@@ -347,7 +347,9 @@ gfxFont::Measure(gfxTextRun *aTextRun,
     metrics.mAdvanceWidth = floatAdvance;
     const PRUint32 appUnitsPerDevUnit = aTextRun->GetAppUnitsPerDevUnit();
     metrics.mAscent = fontMetrics.maxAscent*appUnitsPerDevUnit;
-    metrics.mDescent = fontMetrics.maxDescent*appUnitsPerDevUnit;
+    gfxFloat descentForUnderline =
+        NS_round(fontMetrics.underlineSize) + NS_round(metrics.mAscent - fontMetrics.underlineOffset) - metrics.mAscent;
+    metrics.mDescent = PR_MAX(fontMetrics.maxDescent, descentForUnderline)*appUnitsPerDevUnit;
     metrics.mBoundingBox =
         gfxRect(0, -metrics.mAscent, floatAdvance, metrics.mAscent + metrics.mDescent);
     return metrics;
diff --git a/mozilla/layout/base/nsPresContext.h b/mozilla/layout/base/nsPresContext.h
index 7c48a269d67..88639cd874b 100644
--- a/mozilla/layout/base/nsPresContext.h
+++ b/mozilla/layout/base/nsPresContext.h
@@ -518,6 +518,9 @@ public:
   float AppUnitsToPoints(nscoord aAppUnits) const
   { return (float)aAppUnits / mDeviceContext->AppUnitsPerInch() * 72.0f; }
 
+  nscoord RoundAppUnitsToNearestDevPixels(nscoord aAppUnits) const
+  { return DevPixelsToAppUnits(AppUnitsToDevPixels(aAppUnits)); }
+
   /**
    * Get the language-specific transform type for the current document.
    * This tells us whether we need to perform special language-dependent
diff --git a/mozilla/layout/generic/nsInlineFrame.cpp b/mozilla/layout/generic/nsInlineFrame.cpp
index 24afa010e0d..4a34f8e1ec9 100644
--- a/mozilla/layout/generic/nsInlineFrame.cpp
+++ b/mozilla/layout/generic/nsInlineFrame.cpp
@@ -559,6 +559,15 @@ nsInlineFrame::ReflowFrames(nsPresContext* aPresContext,
     // affect our height.
     fm->GetMaxAscent(aMetrics.ascent);
     fm->GetHeight(aMetrics.height);
+    // Include the text-decoration lines to the height.
+    // Currently, only undeline is overflowable.
+    nscoord offset, size;
+    fm->GetUnderline(offset, size);
+    nscoord ascentAndUnderline =
+      aPresContext->RoundAppUnitsToNearestDevPixels(aMetrics.ascent - offset) +
+      aPresContext->RoundAppUnitsToNearestDevPixels(size);
+    if (ascentAndUnderline > aMetrics.height)
+      aMetrics.height = ascentAndUnderline;
   } else {
     NS_WARNING("Cannot get font metrics - defaulting sizes to 0");
     aMetrics.ascent = aMetrics.height = 0;