diff --git a/package.json b/package.json
index 76354ea70..43ce82fb7 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@arbitrum/nitro-contracts",
-  "version": "2.1.1",
+  "version": "2.1.2",
   "description": "Layer 2 precompiles and rollup for Arbitrum Nitro",
   "author": "Offchain Labs, Inc.",
   "license": "BUSL-1.1",
diff --git a/src/bridge/ERC20Bridge.sol b/src/bridge/ERC20Bridge.sol
index d2d3bffc2..727c3a7fd 100644
--- a/src/bridge/ERC20Bridge.sol
+++ b/src/bridge/ERC20Bridge.sol
@@ -62,6 +62,15 @@ contract ERC20Bridge is AbsBridge, IERC20Bridge {
         }
     }
 
+    /// @notice When upgrading a custom fee chain from v1.x.x to v2.1.2, nativeTokenDecimals must be set to 18.
+    ///         This is because v1.x.x contracts assume 18 decimals, but the ERC20Bridge does not have the decimals set in storage.
+    function postUpgradeInit() external onlyDelegated onlyProxyOwner {
+        // this zero check might save you from accidentally upgrading from v2.x.x to v2.1.2
+        // it will not save you if your native token is supposed to have 0 decimals
+        require(nativeTokenDecimals == 0, "NONZERO_NATIVE_TOKEN_DECIMALS");
+        nativeTokenDecimals = 18;
+    }
+
     /// @inheritdoc IERC20Bridge
     function enqueueDelayedMessage(
         uint8 kind,
diff --git a/test/signatures/ERC20Bridge b/test/signatures/ERC20Bridge
index f7839312f..b47e657b7 100644
--- a/test/signatures/ERC20Bridge
+++ b/test/signatures/ERC20Bridge
@@ -13,6 +13,7 @@
   "initialize(address,address)": "485cc955",
   "nativeToken()": "e1758bd8",
   "nativeTokenDecimals()": "ad48cb5e",
+  "postUpgradeInit()": "95fcea78",
   "rollup()": "cb23bcb5",
   "sequencerInbox()": "ee35f327",
   "sequencerInboxAccs(uint256)": "16bf5579",