2 files changed, 17 insertions, 13 deletions
diff --git a/packages/contracts/test/exchange/internal.ts b/packages/contracts/test/exchange/internal.ts
index 67d1d2d2c..0231cc3f1 100644
--- a/packages/contracts/test/exchange/internal.ts
+++ b/packages/contracts/test/exchange/internal.ts
@@ -63,6 +63,7 @@ describe('Exchange core internal functions', () => {
     let testExchange: TestExchangeInternalsContract;
     let invalidOpcodeErrorForCall: Error | undefined;
     let overflowErrorForSendTransaction: Error | undefined;
+    let divisionByZeroErrorForCall: Error | undefined;
 
     before(async () => {
         await blockchainLifecycle.startAsync();
@@ -79,6 +80,9 @@ describe('Exchange core internal functions', () => {
         overflowErrorForSendTransaction = new Error(
             await getRevertReasonOrErrorMessageForSendTransactionAsync(RevertReason.Uint256Overflow),
         );
+        divisionByZeroErrorForCall = new Error(
+            await getRevertReasonOrErrorMessageForSendTransactionAsync(RevertReason.DivisionByZero),
+        );
         invalidOpcodeErrorForCall = new Error(await getInvalidOpcodeErrorMessageForCallAsync());
     });
     // Note(albrow): Don't forget to add beforeEach and afterEach calls to reset
@@ -215,26 +219,26 @@ describe('Exchange core internal functions', () => {
             denominator: BigNumber,
             target: BigNumber,
         ): Promise<boolean> {
-            const product = numerator.mul(target);
             if (denominator.eq(0)) {
-                throw invalidOpcodeErrorForCall;
+                throw divisionByZeroErrorForCall;
             }
-            const remainder = product.mod(denominator);
-            if (remainder.eq(0)) {
+            if (numerator.eq(0)) {
+                return false;
+            }
+            if (target.eq(0)) {
                 return false;
             }
+            const product = numerator.mul(target);
+            const remainder = product.mod(denominator);
+            const remainderTimes1000 = remainder.mul('1000');
+            const isError = remainderTimes1000.gt(product);
             if (product.greaterThan(MAX_UINT256)) {
                 throw overflowErrorForCall;
             }
-            if (product.eq(0)) {
-                throw invalidOpcodeErrorForCall;
-            }
-            const remainderTimes1000000 = remainder.mul('1000000');
-            if (remainderTimes1000000.greaterThan(MAX_UINT256)) {
+            if (remainderTimes1000.greaterThan(MAX_UINT256)) {
                 throw overflowErrorForCall;
             }
-            const errPercentageTimes1000000 = remainderTimes1000000.dividedToIntegerBy(product);
-            return errPercentageTimes1000000.greaterThan('1000');
+            return isError;
         }
         async function testIsRoundingErrorAsync(
             numerator: BigNumber,
diff --git a/packages/contracts/test/exchange/libs.ts b/packages/contracts/test/exchange/libs.ts
index 6c3305d1d..c08d62758 100644
--- a/packages/contracts/test/exchange/libs.ts
+++ b/packages/contracts/test/exchange/libs.ts
@@ -71,13 +71,13 @@ describe('Exchange libs', () => {
     // combinatorial tests in test/exchange/internal. They test specific edge
     // cases that are not covered by the combinatorial tests.
     describe('LibMath', () => {
-        it('should return false if there is a rounding error of 0.1%', async () => {
+        it('should return true if there is a rounding error of 0.1%', async () => {
             const numerator = new BigNumber(20);
             const denominator = new BigNumber(999);
             const target = new BigNumber(50);
             // rounding error = ((20*50/999) - floor(20*50/999)) / (20*50/999) = 0.1%
             const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
-            expect(isRoundingError).to.be.false();
+            expect(isRoundingError).to.be.true();
         });
         it('should return false if there is a rounding of 0.09%', async () => {
             const numerator = new BigNumber(20);