diff --git a/gfx/2d/BaseMargin.h b/gfx/2d/BaseMargin.h
index cf111f96a36b..469541e6177b 100644
--- a/gfx/2d/BaseMargin.h
+++ b/gfx/2d/BaseMargin.h
@@ -76,8 +76,8 @@ struct BaseMargin {
     left = aLeft;
   }
 
-  T LeftRight() const { return left + right; }
-  T TopBottom() const { return top + bottom; }
+  Coord LeftRight() const { return left + right; }
+  Coord TopBottom() const { return top + bottom; }
 
   Coord& Side(SideT aSide) {
     // This is ugly!