diff --git a/gfx/public/nsIFontMetrics.h b/gfx/public/nsIFontMetrics.h
index e71f4a7b50a..74d709a2e72 100644
--- a/gfx/public/nsIFontMetrics.h
+++ b/gfx/public/nsIFontMetrics.h
@@ -154,6 +154,13 @@ public:
    * Returns the font handle associated with these metrics
    */
   NS_IMETHOD  GetFontHandle(nsFontHandle &aHandle) = 0;
+
+#ifdef _WIN32
+  /**
+   * Returns the average character width
+   */
+  NS_IMETHOD  GetAveCharWidth(nscoord& aAveCharWidth) = 0;
+#endif
 };
 
 #endif /* nsIFontMetrics_h___ */
diff --git a/gfx/src/windows/nsFontMetricsWin.cpp b/gfx/src/windows/nsFontMetricsWin.cpp
index 19d5c128b5b..328f2d6edac 100644
--- a/gfx/src/windows/nsFontMetricsWin.cpp
+++ b/gfx/src/windows/nsFontMetricsWin.cpp
@@ -2524,6 +2524,7 @@ HDC   dc1 = NULL;
   mMaxAscent = NSToCoordRound(metrics.tmAscent * dev2app);
   mMaxDescent = NSToCoordRound(metrics.tmDescent * dev2app);
   mMaxAdvance = NSToCoordRound(metrics.tmMaxCharWidth * dev2app);
+  mAveCharWidth = NSToCoordRound(metrics.tmAveCharWidth * dev2app);
 
    // Cache the width of a single space.
   SIZE  size;
@@ -2647,6 +2648,13 @@ nsFontMetricsWin::GetFontHandle(nsFontHandle &aHandle)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsFontMetricsWin::GetAveCharWidth(nscoord &aAveCharWidth)
+{
+  aAveCharWidth = mAveCharWidth;
+  return NS_OK;
+}
+
 nsFontWin::nsFontWin(LOGFONT* aLogFont, HFONT aFont, PRUint32* aMap)
 {
   if (aLogFont) {
@@ -2678,7 +2686,6 @@ nsFontWinUnicode::GetWidth(HDC aDC, const PRUnichar* aString, PRUint32 aLength)
 {
   SIZE size;
   ::GetTextExtentPoint32W(aDC, aString, aLength, &size);
-
   return size.cx;
 }
 
diff --git a/gfx/src/windows/nsFontMetricsWin.h b/gfx/src/windows/nsFontMetricsWin.h
index 388935b94ae..d3accaf94bf 100644
--- a/gfx/src/windows/nsFontMetricsWin.h
+++ b/gfx/src/windows/nsFontMetricsWin.h
@@ -123,6 +123,7 @@ public:
   NS_IMETHOD  GetFont(const nsFont *&aFont);
   NS_IMETHOD  GetLangGroup(nsIAtom** aLangGroup);
   NS_IMETHOD  GetFontHandle(nsFontHandle &aHandle);
+  NS_IMETHOD  GetAveCharWidth(nscoord &aAveCharWidth);
 
   virtual nsresult   GetSpaceWidth(nscoord &aSpaceWidth);
   virtual nsFontWin* FindGlobalFont(HDC aDC, PRUnichar aChar);
@@ -199,6 +200,7 @@ protected:
   nscoord             mMaxAscent;
   nscoord             mMaxDescent;
   nscoord             mMaxAdvance;
+  nscoord             mAveCharWidth;
 #ifdef MOZ_MATHML
   float               mItalicSlope;
 #endif