diff --git a/contracts/token/ApprovalReceiver.sol b/contracts/token/ApprovalReceiver.sol
new file mode 100644
index 0000000..866e1b0
--- /dev/null
+++ b/contracts/token/ApprovalReceiver.sol
@@ -0,0 +1,5 @@
+pragma solidity ^0.4.11;
+
+contract ApprovalReceiver {
+  function receiveApproval(address from, uint value, address tokenContract, bytes extraData) returns (bool);
+}
diff --git a/contracts/token/StandardToken.sol b/contracts/token/StandardToken.sol
index b80c513..484cfeb 100644
--- a/contracts/token/StandardToken.sol
+++ b/contracts/token/StandardToken.sol
@@ -9,25 +9,34 @@ contract StandardToken is ERC20Token {
     mapping (address => mapping (address => uint256)) allowed;
 
     constructor() internal { }
-    
+
     function transfer(
         address _to,
         uint256 _value
-    ) 
-        external 
+    )
+        external
         returns (bool success)
     {
-        return transfer(msg.sender, _to, _value);    
+        return transfer(msg.sender, _to, _value);
     }
 
-    function approve(address _spender, uint256 _value) 
-        external
-        returns (bool success) 
-    {
-        allowed[msg.sender][_spender] = _value;
-        emit Approval(msg.sender, _spender, _value);
-        return true;
-    }
+    /**
+     * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
+     * @param _spender The address which will spend the funds.
+     * @param _value The amount of tokens to be spent.
+     */
+    function approve(address _spender, uint256 _value) returns (bool) {
+
+      // To change the approve amount you first have to reduce the addresses`
+      //  allowance to zero by calling `approve(_spender, 0)` if it is not
+      //  already 0 to mitigate the race condition described here:
+      //  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
+      require((_value == 0) || (allowed[msg.sender][_spender] == 0));
+
+      allowed[msg.sender][_spender] = _value;
+      Approval(msg.sender, _spender, _value);
+      return true;
+  }
 
     function transferFrom(
         address _from,
@@ -38,35 +47,35 @@ contract StandardToken is ERC20Token {
         returns (bool success)
     {
         if (balances[_from] >= _value &&
-            allowed[_from][msg.sender] >= _value && 
+            allowed[_from][msg.sender] >= _value &&
             _value > 0) {
             allowed[_from][msg.sender] -= _value;
             return transfer(_from, _to, _value);
-        } else { 
-            return false; 
+        } else {
+            return false;
         }
     }
 
-    function allowance(address _owner, address _spender) 
-        external 
-        view 
+    function allowance(address _owner, address _spender)
+        external
+        view
         returns (uint256 remaining)
     {
         return allowed[_owner][_spender];
     }
 
-    function balanceOf(address _owner) 
-        external 
-        view 
-        returns (uint256 balance) 
+    function balanceOf(address _owner)
+        external
+        view
+        returns (uint256 balance)
     {
         return balances[_owner];
     }
-    
-    function totalSupply() 
-        external 
-        view 
-        returns(uint256 currentTotalSupply) 
+
+    function totalSupply()
+        external
+        view
+        returns(uint256 currentTotalSupply)
     {
         return supply;
     }
@@ -74,7 +83,7 @@ contract StandardToken is ERC20Token {
     function mint(
         address _to,
         uint256 _amount
-    ) 
+    )
         internal
     {
         balances[_to] += _amount;
@@ -83,11 +92,11 @@ contract StandardToken is ERC20Token {
     }
 
     function transfer(
-        address _from, 
+        address _from,
         address _to,
         uint256 _value
     )
-        internal 
+        internal
         returns (bool success)
     {
         if (balances[_from] >= _value && _value > 0) {
@@ -95,8 +104,8 @@ contract StandardToken is ERC20Token {
             balances[_to] += _value;
             emit Transfer(_from, _to, _value);
             return true;
-        } else { 
-            return false; 
+        } else {
+            return false;
         }
     }
 
diff --git a/contracts/token/TestToken.sol b/contracts/token/TestToken.sol
index 2afff21..0845c45 100644
--- a/contracts/token/TestToken.sol
+++ b/contracts/token/TestToken.sol
@@ -1,19 +1,26 @@
 pragma solidity ^0.4.23;
 
 import "./StandardToken.sol";
+import './ApprovalReceiver.sol';
 
 /**
  * @notice ERC20Token for test scripts, can be minted by anyone.
  */
 contract TestToken is StandardToken {
-    
+
     constructor() public { }
 
     /**
-     * @notice any caller can mint any `_amount` 
+     * @notice any caller can mint any `_amount`
      * @param _amount how much to be minted
      */
     function mint(uint256 _amount) public {
         mint(msg.sender, _amount);
     }
+
+    function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
+      assert(approve(_spender, _value));
+      return ApprovalReceiver(_spender).receiveApproval(msg.sender, _value, this, _extraData);
+    }
+
 }