diff --git a/content/svg/content/src/nsSVGPreserveAspectRatio.cpp b/content/svg/content/src/nsSVGPreserveAspectRatio.cpp
index 8beedd77b57..5e60b36720d 100644
--- a/content/svg/content/src/nsSVGPreserveAspectRatio.cpp
+++ b/content/svg/content/src/nsSVGPreserveAspectRatio.cpp
@@ -202,6 +202,7 @@ nsSVGPreserveAspectRatio::SetBaseValueString(const nsAString &aValueAsString,
   }
 
   mAnimVal = mBaseVal = val;
+  aSVGElement->DidChangePreserveAspectRatio(aDoSetAttr);
   return NS_OK;
 }
 
diff --git a/content/svg/content/src/nsSVGSVGElement.cpp b/content/svg/content/src/nsSVGSVGElement.cpp
index 3ad5fddd621..ebbedf7ae42 100644
--- a/content/svg/content/src/nsSVGSVGElement.cpp
+++ b/content/svg/content/src/nsSVGSVGElement.cpp
@@ -1292,7 +1292,7 @@ nsSVGSVGElement::GetViewboxToViewportTransform(nsIDOMSVGMatrix **_retval)
   }
 
   nsSVGViewBoxRect viewbox;
-  if (HasAttr(kNameSpaceID_None, nsGkAtoms::viewBox)) {
+  if (mViewBox.IsValid()) {
     viewbox = mViewBox.GetAnimValue();
   } else {
     viewbox.x = viewbox.y = 0.0f;
@@ -1461,7 +1461,7 @@ nsSVGSVGElement::GetLength(PRUint8 aCtxType)
 {
   float h, w;
 
-  if (HasAttr(kNameSpaceID_None, nsGkAtoms::viewBox)) {
+  if (mViewBox.IsValid()) {
     const nsSVGViewBoxRect& viewbox = mViewBox.GetAnimValue();
     w = viewbox.width;
     h = viewbox.height;
diff --git a/content/svg/content/src/nsSVGViewBox.cpp b/content/svg/content/src/nsSVGViewBox.cpp
index d14afacca13..cd07b4b53d2 100644
--- a/content/svg/content/src/nsSVGViewBox.cpp
+++ b/content/svg/content/src/nsSVGViewBox.cpp
@@ -20,7 +20,7 @@
  * the Initial Developer. All Rights Reserved.
  *
  * Contributor(s):
- *   Jonathan Watt <jonathan.watt@strath.ac.uk> (original author)
+ *   Craig Topper <craig.topper@gmail.com> (original author)
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either of the GNU General Public License Version 2 or later (the "GPL"),
@@ -78,6 +78,7 @@ nsSVGViewBox::Init()
 {
   mBaseVal = nsSVGViewBoxRect();
   mAnimVal = nsnull;
+  mHasBaseVal = PR_FALSE;
 }
 
 const nsSVGViewBoxRect&
@@ -94,10 +95,8 @@ nsSVGViewBox::SetBaseValue(float aX, float aY, float aWidth, float aHeight,
                            nsSVGElement *aSVGElement, PRBool aDoSetAttr)
 {
   mAnimVal = nsnull;
-  mBaseVal.x = aX;
-  mBaseVal.y = aY;
-  mBaseVal.width  = aWidth;
-  mBaseVal.height = aHeight;
+  mBaseVal = nsSVGViewBoxRect(aX, aY, aWidth, aHeight);
+  mHasBaseVal = PR_TRUE;
 
   aSVGElement->DidChangeViewBox(aDoSetAttr);
 }
@@ -128,11 +127,7 @@ nsSVGViewBox::SetBaseValueString(const nsAString& aValue,
     // there was a parse error.
     rv = NS_ERROR_FAILURE;
   } else {
-    mAnimVal = nsnull;
-    mBaseVal.x = vals[0];
-    mBaseVal.y = vals[1];
-    mBaseVal.width = vals[2];
-    mBaseVal.height = vals[3];
+    SetBaseValue(vals[0], vals[1], vals[2], vals[3], aSVGElement, aDoSetAttr);
   }
 
   nsMemory::Free(str);
diff --git a/content/svg/content/src/nsSVGViewBox.h b/content/svg/content/src/nsSVGViewBox.h
index eb1a93489fb..c37025a1a67 100644
--- a/content/svg/content/src/nsSVGViewBox.h
+++ b/content/svg/content/src/nsSVGViewBox.h
@@ -20,7 +20,7 @@
  * the Initial Developer. All Rights Reserved.
  *
  * Contributor(s):
- *   Jonathan Watt <jonathan.watt@strath.ac.uk> (original author)
+ *   Craig Topper <craig.topper@gmail.com> (original author)
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either of the GNU General Public License Version 2 or later (the "GPL"),
@@ -61,6 +61,10 @@ public:
 
   void Init();
 
+  // Used by element to tell if viewbox is defined
+  PRBool IsValid() const
+    { return (mHasBaseVal || mAnimVal); }
+
   const nsSVGViewBoxRect& GetBaseValue() const
     { return mBaseVal; }
   void SetBaseValue(float aX, float aY, float aWidth, float aHeight,
@@ -80,6 +84,7 @@ private:
 
   nsSVGViewBoxRect mBaseVal;
   nsAutoPtr<nsSVGViewBoxRect> mAnimVal;
+  PRPackedBool mHasBaseVal;
 
   struct DOMBaseVal : public nsIDOMSVGRect
   {