modified   contracts/lib/OrderValidator.sol
@@ -225,6 +225,8 @@ contract OrderValidator is Executor, ZoneInteraction {
                 // Update order status and fill amount, packing struct values.
                 _orderStatus[orderHash].isValidated = true;
                 _orderStatus[orderHash].isCancelled = false;
+                require(filledNumerator + numerator <= type(uint120).max, "overflow");
+                require(denominator <= type(uint120).max, "overflow");
                 _orderStatus[orderHash].numerator = uint120(
                     filledNumerator + numerator
                 );
@@ -234,6 +236,8 @@ contract OrderValidator is Executor, ZoneInteraction {
             // Update order status and fill amount, packing struct values.
             _orderStatus[orderHash].isValidated = true;
             _orderStatus[orderHash].isCancelled = false;
+            require(numerator <= type(uint120).max, "overflow");
+            require(denominator <= type(uint120).max, "overflow");
             _orderStatus[orderHash].numerator = uint120(numerator);
             _orderStatus[orderHash].denominator = uint120(denominator);
         }
