diff --git a/gfx/src/nsRect.cpp b/gfx/src/nsRect.cpp
index e16d489ac641..d4595b801b38 100644
--- a/gfx/src/nsRect.cpp
+++ b/gfx/src/nsRect.cpp
@@ -328,3 +328,15 @@ PRBool nsIntRect::UnionRect(const nsIntRect &aRect1, const nsIntRect &aRect2)
   return result;
 }
 
+// scale the rect but round to smallest containing rect
+nsIntRect& nsIntRect::ScaleRoundOut(float aXScale, float aYScale)
+{
+  nscoord right = NSToCoordCeil(float(XMost()) * aXScale);
+  nscoord bottom = NSToCoordCeil(float(YMost()) * aYScale);
+  x = NSToCoordFloor(float(x) * aXScale);
+  y = NSToCoordFloor(float(y) * aYScale);
+  width = (right - x);
+  height = (bottom - y);
+  return *this;
+}
+
diff --git a/gfx/src/nsRect.h b/gfx/src/nsRect.h
index e02e17b6a456..a7d1490d4fbb 100644
--- a/gfx/src/nsRect.h
+++ b/gfx/src/nsRect.h
@@ -342,6 +342,8 @@ struct NS_GFX nsIntRect {
   PRInt32 YMost() const {return y + height;}
 
   inline nsRect ToAppUnits(nscoord aAppUnitsPerPixel) const;
+
+  nsIntRect& ScaleRoundOut(float aXScale, float aYScale);
 
   // Returns a special nsIntRect that's used in some places to signify
   // "all available space".
diff --git a/gfx/src/nsRegion.cpp b/gfx/src/nsRegion.cpp
index cb5ef38383cd..fe801ada38ac 100644
--- a/gfx/src/nsRegion.cpp
+++ b/gfx/src/nsRegion.cpp
@@ -1316,6 +1316,22 @@ nsRegion& nsRegion::ExtendForScaling (float aXMult, float aYMult)
   *this = region;
   return *this;
 }
+
+nsRegion& nsRegion::ScaleRoundOut (float aXScale, float aYScale)
+{
+  nsRegion region;
+  nsRegionRectIterator iter(*this);
+  for (;;) {
+    const nsRect* r = iter.Next();
+    if (!r)
+      break;
+    nsRect rect = *r;
+    rect.ScaleRoundOut(aXScale, aYScale);
+    region.Or(region, rect);
+  }
+  *this = region;
+  return *this;
+}
 
 nsRegion nsRegion::ConvertAppUnitsRoundOut (PRInt32 aFromAPP, PRInt32 aToAPP) const
 {
diff --git a/gfx/src/nsRegion.h b/gfx/src/nsRegion.h
index a25daf53f6f7..96a3731ffc19 100644
--- a/gfx/src/nsRegion.h
+++ b/gfx/src/nsRegion.h
@@ -184,6 +184,7 @@ public:
   // the region.
   nsRegion ConvertAppUnitsRoundOut (PRInt32 aFromAPP, PRInt32 aToAPP) const;
   nsRegion ConvertAppUnitsRoundIn (PRInt32 aFromAPP, PRInt32 aToAPP) const;
+  nsRegion& ScaleRoundOut(float aXScale, float aYScale);
   nsIntRegion ToOutsidePixels (nscoord aAppUnitsPerPixel) const;
   nsRegion& ExtendForScaling (float aXMult, float aYMult);
 
@@ -438,6 +439,12 @@ public:
   {
     return FromRect (mImpl.GetLargestRectangle( ToRect(aContainingRect) ));
   }
+
+  nsIntRegion& ScaleRoundOut (float aXScale, float aYScale)
+  {
+    mImpl.ScaleRoundOut(aXScale, aYScale);
+    return *this;
+  }
 
   nsIntRegion& ExtendForScaling (float aXMult, float aYMult)
   {