diff --git a/contracts/DODOEthProxy.sol b/contracts/DODOEthProxy.sol
index a619be1..aebaa52 100644
--- a/contracts/DODOEthProxy.sol
+++ b/contracts/DODOEthProxy.sol
@@ -15,12 +15,10 @@ import {IDODO} from "./intf/IDODO.sol";
 import {IERC20} from "./intf/IERC20.sol";
 import {IWETH} from "./intf/IWETH.sol";
 
-
 interface IDODOZoo {
     function getDODO(address baseToken, address quoteToken) external view returns (address);
 }
 
-
 /**
  * @title DODO Eth Proxy
  * @author DODO Breeder
@@ -112,7 +110,7 @@ contract DODOEthProxy is ReentrancyGuard {
         require(DODO != address(0), "DODO_NOT_EXIST");
         payTokenAmount = IDODO(DODO).queryBuyBaseToken(ethAmount);
         _transferIn(quoteTokenAddress, msg.sender, payTokenAmount);
-        IERC20(quoteTokenAddress).approve(DODO, payTokenAmount);
+        IERC20(quoteTokenAddress).safeApprove(DODO, payTokenAmount);
         IDODO(DODO).buyBaseToken(ethAmount, maxPayTokenAmount, "");
         IWETH(_WETH_).withdraw(ethAmount);
         msg.sender.transfer(ethAmount);
@@ -127,7 +125,7 @@ contract DODOEthProxy is ReentrancyGuard {
     ) external preventReentrant returns (uint256 receiveEthAmount) {
         address DODO = IDODOZoo(_DODO_ZOO_).getDODO(baseTokenAddress, _WETH_);
         require(DODO != address(0), "DODO_NOT_EXIST");
-        IERC20(baseTokenAddress).approve(DODO, tokenAmount);
+        IERC20(baseTokenAddress).safeApprove(DODO, tokenAmount);
         _transferIn(baseTokenAddress, msg.sender, tokenAmount);
         receiveEthAmount = IDODO(DODO).sellBaseToken(tokenAmount, minReceiveEthAmount, "");
         IWETH(_WETH_).withdraw(receiveEthAmount);
diff --git a/contracts/lib/SafeERC20.sol b/contracts/lib/SafeERC20.sol
index 09440bf..67a0188 100644
--- a/contracts/lib/SafeERC20.sol
+++ b/contracts/lib/SafeERC20.sol
@@ -45,6 +45,22 @@ library SafeERC20 {
         );
     }
 
+    function safeApprove(
+        IERC20 token,
+        address spender,
+        uint256 value
+    ) internal {
+        // safeApprove should only be called when setting an initial allowance,
+        // or when resetting it to zero. To increase and decrease it, use
+        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
+        // solhint-disable-next-line max-line-length
+        require(
+            (value == 0) || (token.allowance(address(this), spender) == 0),
+            "SafeERC20: approve from non-zero to non-zero allowance"
+        );
+        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
+    }
+
     /**
      * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
      * on the return value: the return value is optional (but if data is returned, it must not be false).
diff --git a/test/DODOEthProxyAsBase.test.ts b/test/DODOEthProxyAsBase.test.ts
index 010ed7b..e72babc 100644
--- a/test/DODOEthProxyAsBase.test.ts
+++ b/test/DODOEthProxyAsBase.test.ts
@@ -101,14 +101,14 @@ describe("DODO ETH PROXY", () => {
   describe("buy&sell eth directly", () => {
     it("buy", async () => {
       const buyAmount = "1";
-      logGas(
-        await DODOEthProxy.methods
+      await logGas(
+        DODOEthProxy.methods
           .buyEthWithToken(
             ctx.QUOTE.options.address,
             decimalStr(buyAmount),
             decimalStr("200")
-          )
-          .send(ctx.sendParam(trader)),
+          ),
+        ctx.sendParam(trader),
         "buy ETH with token directly"
       );
       assert.strictEqual(
@@ -122,14 +122,14 @@ describe("DODO ETH PROXY", () => {
     });
     it("sell", async () => {
       const sellAmount = "1";
-      logGas(
-        await DODOEthProxy.methods
+      await logGas(
+        DODOEthProxy.methods
           .sellEthToToken(
             ctx.QUOTE.options.address,
             decimalStr(sellAmount),
             decimalStr("50")
-          )
-          .send(ctx.sendParam(trader, sellAmount)),
+          ),
+        ctx.sendParam(trader, sellAmount),
         "sell ETH to token directly"
       );
       assert.strictEqual(
diff --git a/test/DODOEthProxyAsQuote.test.ts b/test/DODOEthProxyAsQuote.test.ts
index 985a8b4..04b1932 100644
--- a/test/DODOEthProxyAsQuote.test.ts
+++ b/test/DODOEthProxyAsQuote.test.ts
@@ -103,14 +103,12 @@ describe("DODO ETH PROXY", () => {
       const maxPayEthAmount = "2.1";
       const ethInPoolBefore = decimalStr("10");
       const traderEthBalanceBefore = await ctx.Web3.eth.getBalance(trader);
-      const txReceipt: TransactionReceipt = await DODOEthProxy.methods
+      const txReceipt: TransactionReceipt = await logGas(DODOEthProxy.methods
         .buyTokenWithEth(
           ctx.BASE.options.address,
           decimalStr("200"),
           decimalStr(maxPayEthAmount)
-        )
-        .send(ctx.sendParam(trader, maxPayEthAmount));
-      logGas(txReceipt, "buy token with ETH directly");
+        ), ctx.sendParam(trader, maxPayEthAmount), "buy token with ETH directly");
       const ethInPoolAfter = "12056338203652739553";
       assert.strictEqual(
         await ctx.DODO.methods._QUOTE_BALANCE_().call(),
@@ -134,14 +132,14 @@ describe("DODO ETH PROXY", () => {
     });
     it("sell", async () => {
       const minReceiveEthAmount = "0.45";
-      logGas(
-        await DODOEthProxy.methods
+      await logGas(
+        DODOEthProxy.methods
           .sellTokenToEth(
             ctx.BASE.options.address,
             decimalStr("50"),
             decimalStr(minReceiveEthAmount)
-          )
-          .send(ctx.sendParam(trader)),
+          ),
+        ctx.sendParam(trader),
         "sell token to ETH directly"
       );
       assert.strictEqual(
diff --git a/test/utils/Log.ts b/test/utils/Log.ts
index c2bc65d..7e7c3b7 100644
--- a/test/utils/Log.ts
+++ b/test/utils/Log.ts
@@ -5,15 +5,15 @@
 
 */
 
-import { TransactionReceipt } from "web3-core"
-
 export const blueText = x => `\x1b[36m${x}\x1b[0m`;
 export const yellowText = x => `\x1b[33m${x}\x1b[0m`;
 export const greenText = x => `\x1b[32m${x}\x1b[0m`;
 export const redText = x => `\x1b[31m${x}\x1b[0m`;
 export const numberWithCommas = x => x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
 
-export function logGas(receipt: TransactionReceipt, desc: string) {
+export async function logGas(funcCall: any, params: any, desc: string) {
+  const estimatedGas = await funcCall.estimateGas(params)
+  const receipt = await funcCall.send(params)
   const gasUsed = receipt.gasUsed;
   let colorFn;
 
@@ -25,5 +25,6 @@ export function logGas(receipt: TransactionReceipt, desc: string) {
     colorFn = redText;
   }
 
-  console.log(("Gas used:").padEnd(60, '.'), blueText(desc) + "  ", colorFn(numberWithCommas(gasUsed).padStart(5)));
+  console.log(("Gas estimated:" + numberWithCommas(estimatedGas)).padEnd(60, '.'), blueText(desc) + "  ", colorFn(numberWithCommas(gasUsed).padStart(5)));
+  return receipt
 }
\ No newline at end of file