diff --git a/gfx/src/FilterSupport.cpp b/gfx/src/FilterSupport.cpp
index 67b96a3d7346..5dab0a52b8e9 100644
--- a/gfx/src/FilterSupport.cpp
+++ b/gfx/src/FilterSupport.cpp
@@ -986,7 +986,6 @@ ElementForIndex(int32_t aIndex,
 {
   switch (aIndex) {
     case FilterPrimitiveDescription::kPrimitiveIndexSourceGraphic:
-    case FilterPrimitiveDescription::kPrimitiveIndexSourceAlpha:
       return aSourceGraphicElement;
     case FilterPrimitiveDescription::kPrimitiveIndexFillPaint:
       return aFillPaintElement;
@@ -1103,10 +1102,6 @@ FilterNodeGraphFromDescription(DrawTarget* aDT,
           if (surf) {
             IntPoint offset = surfaceRect.TopLeft();
             sourceFilterNode = FilterWrappers::ForSurface(aDT, surf, offset);
-
-            if (inputIndex == FilterPrimitiveDescription::kPrimitiveIndexSourceAlpha) {
-              sourceFilterNode = FilterWrappers::ToAlpha(aDT, sourceFilterNode);
-            }
           }
 
           inputFilter = new FilterCachedColorModels(aDT, sourceFilterNode,
diff --git a/gfx/src/FilterSupport.h b/gfx/src/FilterSupport.h
index 1ff92441b5dc..688b8bb42f12 100644
--- a/gfx/src/FilterSupport.h
+++ b/gfx/src/FilterSupport.h
@@ -284,9 +284,8 @@ class FilterPrimitiveDescription MOZ_FINAL {
 public:
   enum {
     kPrimitiveIndexSourceGraphic = -1,
-    kPrimitiveIndexSourceAlpha = -2,
-    kPrimitiveIndexFillPaint = -3,
-    kPrimitiveIndexStrokePaint = -4
+    kPrimitiveIndexFillPaint = -2,
+    kPrimitiveIndexStrokePaint = -3
   };
 
   FilterPrimitiveDescription();
diff --git a/layout/svg/nsSVGFilterInstance.cpp b/layout/svg/nsSVGFilterInstance.cpp
index bcf667a5ceb3..0773af0e4bc7 100644
--- a/layout/svg/nsSVGFilterInstance.cpp
+++ b/layout/svg/nsSVGFilterInstance.cpp
@@ -292,33 +292,31 @@ GetLastResultIndex(const nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs)
 int32_t
 nsSVGFilterInstance::GetOrCreateSourceAlphaIndex(nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs)
 {
-  // If the SourceAlpha index has already been determined or created for this
-  // SVG filter, just return it.
+  // If the SourceAlpha index has already been created for this SVG filter,
+  // return it.
   if (mSourceAlphaAvailable)
     return mSourceAlphaIndex;
 
-  // If this is the first filter in the chain, we can just use the
-  // kPrimitiveIndexSourceAlpha keyword to refer to the SourceAlpha of the
-  // original image.
-  if (mSourceGraphicIndex < 0) {
-    mSourceAlphaIndex = FilterPrimitiveDescription::kPrimitiveIndexSourceAlpha;
-    mSourceAlphaAvailable = true;
-    return mSourceAlphaIndex;
-  }
-
   // Otherwise, create a primitive description to turn the previous filter's
   // output into a SourceAlpha input.
   FilterPrimitiveDescription descr(PrimitiveType::ToAlpha);
   descr.SetInputPrimitive(0, mSourceGraphicIndex);
 
-  const FilterPrimitiveDescription& sourcePrimitiveDescr =
-    aPrimitiveDescrs[mSourceGraphicIndex];
-  descr.SetPrimitiveSubregion(sourcePrimitiveDescr.PrimitiveSubregion());
-  descr.SetIsTainted(sourcePrimitiveDescr.IsTainted());
+  if (mSourceGraphicIndex >= 0) {
+    const FilterPrimitiveDescription& sourcePrimitiveDescr =
+      aPrimitiveDescrs[mSourceGraphicIndex];
+    descr.SetPrimitiveSubregion(sourcePrimitiveDescr.PrimitiveSubregion());
+    descr.SetIsTainted(sourcePrimitiveDescr.IsTainted());
 
-  ColorSpace colorSpace = sourcePrimitiveDescr.OutputColorSpace();
-  descr.SetInputColorSpace(0, colorSpace);
-  descr.SetOutputColorSpace(colorSpace);
+    ColorSpace colorSpace = sourcePrimitiveDescr.OutputColorSpace();
+    descr.SetInputColorSpace(0, colorSpace);
+    descr.SetOutputColorSpace(colorSpace);
+  } else {
+    descr.SetPrimitiveSubregion(ToIntRect(mFilterSpaceBounds));
+    descr.SetIsTainted(true);
+    descr.SetInputColorSpace(0, ColorSpace::SRGB);
+    descr.SetOutputColorSpace(ColorSpace::SRGB);
+  }
 
   aPrimitiveDescrs.AppendElement(descr);
   mSourceAlphaIndex = aPrimitiveDescrs.Length() - 1;