--- a/layout/style/nsCSSValue.h
+++ b/layout/style/nsCSSValue.h
@@ -28,16 +28,20 @@
 #include "nsRefPtrHashtable.h"
 #include "nsString.h"
 #include "nsStringBuffer.h"
 #include "nsTArray.h"
 #include "nsStyleConsts.h"
 #include "nsStyleCoord.h"
 #include "gfxFontFamilyList.h"
 
+#ifndef __GNUC__
+#define __attribute__(x)
+#endif
+
 class imgRequestProxy;
 class nsIContent;
 class nsIDocument;
 class nsIPrincipal;
 class nsIURI;
 class nsPresContext;
 template <class T>
 class nsPtrHashKey;
@@ -1017,17 +1021,18 @@ protected:
     nsCSSValueList* mListDependent;
     nsCSSValueSharedList* MOZ_OWNING_REF mSharedList;
     nsCSSValuePairList_heap* MOZ_OWNING_REF mPairList;
     nsCSSValuePairList* mPairListDependent;
     nsCSSValueFloatColor* MOZ_OWNING_REF mFloatColor;
     mozilla::css::FontFamilyListRefCnt* MOZ_OWNING_REF mFontFamilyList;
     mozilla::css::ComplexColorValue* MOZ_OWNING_REF mComplexColor;
   } mValue;
-};
+
+} __attribute__ ((aligned(4))); /* ensure alignment is at least 4 bytes */
 
 struct nsCSSValue::Array final {
 
   // return |Array| with reference count of zero
   static Array* Create(size_t aItemCount) {
     return new (aItemCount) Array(aItemCount);
   }