diff --git a/src/mocks/Reserve.sol b/src/mocks/Reserve.sol
index d491add..2ad8a1d 100644
--- a/src/mocks/Reserve.sol
+++ b/src/mocks/Reserve.sol
@@ -55,12 +55,15 @@ contract Reserve is ERC20Permit {
     }
 
     function burn(uint256 amount) external payable {
-        (bool sent,) = msg.sender.call{ value: estimateAmount(amount) }("");
-        require(sent, "Failed to send Ether");
         _innerBurn(msg.sender, amount);
+        uint256 valueDiff = address(this).balance - accumulatedDonation;
+        uint256 valueBack = amount * valueDiff / (amount + totalSupply());
+
+        (bool sent,) = msg.sender.call{ value: valueBack }("");
+        require(sent, "Failed to send Ether");
     }
 
-    function estimateAmount(uint256 amount) public view returns (uint256) {
+    function estimateAmount(uint256 amount) external view returns (uint256) {
         uint256 valueDiff = address(this).balance - accumulatedDonation;
         return amount * valueDiff / totalSupply();
     }