--- a/gfx/2d/Types.h
+++ b/gfx/2d/Types.h
@@ -402,19 +402,19 @@ enum SideBits {
 // We use an int32_t helper variable (instead of a Side) for our loop counter,
 // to avoid triggering undefined behavior just before we exit the loop (at
 // which point the counter is incremented beyond the largest valid Side value).
 #define NS_FOR_CSS_SIDES(var_)                                           \
   int32_t MOZ_CONCAT(var_,__LINE__) = mozilla::eSideTop;                 \
   for (mozilla::Side var_;                                               \
        MOZ_CONCAT(var_,__LINE__) <= mozilla::eSideLeft &&                \
          ((var_ = mozilla::Side(MOZ_CONCAT(var_,__LINE__))), true);      \
-       MOZ_CONCAT(var_,__LINE__)++)
+       ++MOZ_CONCAT(var_,__LINE__))
 
-static inline Side operator++(Side& side, int) {
+static inline Side& operator++(Side& side) {
   MOZ_ASSERT(side >= eSideTop && side <= eSideLeft,
              "Out of range side");
   side = Side(side + 1);
   return side;
 }
 
 } // namespace mozilla