diff --git a/src/bridge/AbsOutbox.sol b/src/bridge/AbsOutbox.sol
index 2b87c726..2678f1fb 100644
--- a/src/bridge/AbsOutbox.sol
+++ b/src/bridge/AbsOutbox.sol
@@ -12,7 +12,8 @@ import {
     UnknownRoot,
     AlreadySpent,
     BridgeCallFailed,
-    HadZeroInit
+    HadZeroInit,
+    BadPostUpgradeInit
 } from "../libraries/Error.sol";
 import "./IBridge.sol";
 import "./IOutbox.sol";
@@ -76,6 +77,19 @@ abstract contract AbsOutbox is DelegateCallAware, IOutbox {
         rollup = address(_bridge.rollup());
     }
 
+    function postUpgradeInit() external onlyDelegated onlyProxyOwner {
+        // prevent postUpgradeInit within a withdrawal
+        if (context.l2Block != L2BLOCK_DEFAULT_CONTEXT) revert BadPostUpgradeInit();
+        context = L2ToL1Context({
+            l2Block: L2BLOCK_DEFAULT_CONTEXT,
+            l1Block: L1BLOCK_DEFAULT_CONTEXT,
+            timestamp: TIMESTAMP_DEFAULT_CONTEXT,
+            outputId: OUTPUTID_DEFAULT_CONTEXT,
+            sender: SENDER_DEFAULT_CONTEXT,
+            withdrawalAmount: _defaultContextAmount()
+        });
+    }
+
     function updateSendRoot(bytes32 root, bytes32 l2BlockHash) external {
         if (msg.sender != rollup) revert NotRollup(msg.sender, rollup);
         roots[root] = l2BlockHash;
diff --git a/src/bridge/IOutbox.sol b/src/bridge/IOutbox.sol
index 06358170..be888634 100644
--- a/src/bridge/IOutbox.sol
+++ b/src/bridge/IOutbox.sol
@@ -119,4 +119,10 @@ interface IOutbox {
         uint256 path,
         bytes32 item
     ) external pure returns (bytes32);
+
+    /**
+     * @dev function to be called one time during the outbox upgrade process
+     *      this is used to fix the storage slots
+     */
+    function postUpgradeInit() external;
 }
diff --git a/src/libraries/Error.sol b/src/libraries/Error.sol
index beb0afc8..e4776d80 100644
--- a/src/libraries/Error.sol
+++ b/src/libraries/Error.sol
@@ -7,9 +7,12 @@ pragma solidity ^0.8.4;
 /// @dev Init was already called
 error AlreadyInit();
 
-/// Init was called with param set to zero that must be nonzero
+/// @dev Init was called with param set to zero that must be nonzero
 error HadZeroInit();
 
+/// @dev Thrown when post upgrade init validation fails
+error BadPostUpgradeInit();
+
 /// @dev Thrown when non owner tries to access an only-owner function
 /// @param sender The msg.sender who is not the owner
 /// @param owner The owner address
diff --git a/src/test-helpers/OutboxWithoutOptTester.sol b/src/test-helpers/OutboxWithoutOptTester.sol
index 50f378ac..0036e3c1 100644
--- a/src/test-helpers/OutboxWithoutOptTester.sol
+++ b/src/test-helpers/OutboxWithoutOptTester.sol
@@ -48,6 +48,8 @@ contract OutboxWithoutOptTester is DelegateCallAware, IOutbox {
         rollup = address(_bridge.rollup());
     }
 
+    function postUpgradeInit() external {}
+
     function updateSendRoot(bytes32 root, bytes32 l2BlockHash) external override {
         //if (msg.sender != rollup) revert NotRollup(msg.sender, rollup);  //test only!!!
         roots[root] = l2BlockHash;