diff --git a/contracts/TestERC1271.sol b/contracts/TestERC1271.sol
index 2684bf0..61f7af1 100644
--- a/contracts/TestERC1271.sol
+++ b/contracts/TestERC1271.sol
@@ -28,21 +28,20 @@ contract TestERC1271 is ERC1271 {
     /**
      * Check if a signature is valid
      *
-     * @param _data Data signed over
-     * @param _signature Encoded signature
+     * @param _hash Hash of the data to be signed
+     * @param _signature Signature encoded as (bytes32 r, bytes32 s, uint8 v)
      * @return magicValue Magic value if valid, zero-value otherwise
      */
     function isValidSignature(
-        bytes memory _data,
+        bytes32 _hash,
         bytes memory _signature)
         override
         public
         view
         returns (bytes4 magicValue)
     {
-        bytes32 hash = abi.decode(_data, (bytes32));
         (uint8 v, bytes32 r, bytes32 s) = abi.decode(_signature, (uint8, bytes32, bytes32));
-        if (owner == ecrecover(hash, v, r, s)) {
+        if (owner == ecrecover(_hash, v, r, s)) {
             return MAGICVALUE;
         } else {
             return SIGINVALID;
diff --git a/contracts/exchange/ExchangeCore.sol b/contracts/exchange/ExchangeCore.sol
index ebe675b..f627444 100644
--- a/contracts/exchange/ExchangeCore.sol
+++ b/contracts/exchange/ExchangeCore.sol
@@ -21,7 +21,7 @@ import "../registry/AuthenticatedProxy.sol";
  */
 contract ExchangeCore is ReentrancyGuarded, StaticCaller, EIP712 {
 
-    bytes4 constant internal EIP_1271_MAGICVALUE = 0x20c13b0b;
+    bytes4 constant internal EIP_1271_MAGICVALUE = 0x1626ba7e;
     bytes internal personalSignPrefix = "\x19Ethereum Signed Message:\n";
 
     /* Struct definitions. */
@@ -184,7 +184,7 @@ contract ExchangeCore is ReentrancyGuarded, StaticCaller, EIP712 {
 
         /* (c): Contract-only authentication: EIP/ERC 1271. */
         if (isContract) {
-            if (ERC1271(maker).isValidSignature(abi.encodePacked(calculatedHashToSign), signature) == EIP_1271_MAGICVALUE) {
+            if (ERC1271(maker).isValidSignature(calculatedHashToSign, signature) == EIP_1271_MAGICVALUE) {
                 return true;
             }
             return false;
diff --git a/contracts/lib/EIP1271.sol b/contracts/lib/EIP1271.sol
index 6ebfb96..e968caa 100644
--- a/contracts/lib/EIP1271.sol
+++ b/contracts/lib/EIP1271.sol
@@ -8,23 +8,23 @@ pragma solidity 0.7.5;
 
 abstract contract ERC1271 {
 
-  // bytes4(keccak256("isValidSignature(bytes,bytes)")
-  bytes4 constant internal MAGICVALUE = 0x20c13b0b;
+  // bytes4(keccak256("isValidSignature(bytes32,bytes)")
+  bytes4 constant internal MAGICVALUE = 0x1626ba7e;
 
   /**
-   * @dev Should return whether the signature provided is valid for the provided data
-   * @param _data Arbitrary length data signed on the behalf of address(this)
-   * @param _signature Signature byte array associated with _data
+   * @dev Should return whether the signature provided is valid for the provided hash
+   * @param _hash      Hash of the data to be signed
+   * @param _signature Signature byte array associated with _hash
    *
-   * MUST return the bytes4 magic value 0x20c13b0b when function passes.
+   * MUST return the bytes4 magic value 0x1626ba7e when function passes.
    * MUST NOT modify state (using STATICCALL for solc < 0.5, view modifier for solc > 0.5)
    * MUST allow external calls
-   */
+   */ 
   function isValidSignature(
-      bytes memory _data,
-      bytes memory _signature)
-      virtual
-      public
-      view
-      returns (bytes4 magicValue);
-}
+    bytes32 _hash, 
+    bytes memory _signature)
+    virtual
+    public
+    view 
+    returns (bytes4 magicValue);
+}
\ No newline at end of file
diff --git a/test/4-wyvern-exchange-basics.js b/test/4-wyvern-exchange-basics.js
index ace25f1..e241ce5 100755
--- a/test/4-wyvern-exchange-basics.js
+++ b/test/4-wyvern-exchange-basics.js
@@ -59,7 +59,7 @@ contract('WyvernExchange',accounts => {
 
   it('does not validate order parameters with expirationTime before now',async () => {
     let {exchange,registry} = await withExchangeAndRegistry()
-    let example = {registry: registry.address,maker: accounts[0],staticTarget: exchange.inst.address,staticSelector: '0x00000000',staticExtradata: '0x',maximumFill: '1',listingTime: '0',expirationTime: '0',salt: '0'}
+    let example = {registry: registry.address,maker: accounts[0],staticTarget: exchange.inst.address,staticSelector: '0x00000000',staticExtradata: '0x',maximumFill: '1',listingTime: '0',expirationTime: '1',salt: '0'}
     assert.isFalse(await exchange.validateOrderParameters(example),'Should not have validated')
   })