diff --git a/layout/base/public/nsIScrollableFrame.h b/layout/base/public/nsIScrollableFrame.h
index 4e03dac11fb..feb798e9210 100644
--- a/layout/base/public/nsIScrollableFrame.h
+++ b/layout/base/public/nsIScrollableFrame.h
@@ -70,6 +70,7 @@ public:
     // NS_STYLE_OVERFLOW_AUTO
     PRUint8 mHorizontal, mVertical;
     ScrollbarStyles(PRUint8 h, PRUint8 v) : mHorizontal(h), mVertical(v) {}
+    ScrollbarStyles() {}
   };
 
   virtual ScrollbarStyles GetScrollbarStyles() const = 0;
diff --git a/layout/generic/nsIScrollableFrame.h b/layout/generic/nsIScrollableFrame.h
index 4e03dac11fb..feb798e9210 100644
--- a/layout/generic/nsIScrollableFrame.h
+++ b/layout/generic/nsIScrollableFrame.h
@@ -70,6 +70,7 @@ public:
     // NS_STYLE_OVERFLOW_AUTO
     PRUint8 mHorizontal, mVertical;
     ScrollbarStyles(PRUint8 h, PRUint8 v) : mHorizontal(h), mVertical(v) {}
+    ScrollbarStyles() {}
   };
 
   virtual ScrollbarStyles GetScrollbarStyles() const = 0;