diff --git a/evm/contracts/apps/Base.sol b/evm/contracts/apps/Base.sol
index b8617b1ec5..9d3e5d2f23 100644
--- a/evm/contracts/apps/Base.sol
+++ b/evm/contracts/apps/Base.sol
@@ -67,6 +67,7 @@ abstract contract IBCAppBase is Context, IIBCModule {
     function onChanOpenAck(
         string calldata portId,
         string calldata channelId,
+        string calldata counterpartyChannelId,
         string calldata counterpartyVersion
     ) external virtual override onlyIBC {}
 
diff --git a/evm/contracts/apps/ucs/00-pingpong/PingPong.sol b/evm/contracts/apps/ucs/00-pingpong/PingPong.sol
index e5c6bd85f1..c54d313110 100644
--- a/evm/contracts/apps/ucs/00-pingpong/PingPong.sol
+++ b/evm/contracts/apps/ucs/00-pingpong/PingPong.sol
@@ -153,7 +153,8 @@ contract PingPong is IBCAppBase {
     function onChanOpenAck(
         string calldata _portId,
         string calldata _channelId,
-        string calldata
+        string calldata _counterpartyChannelId,
+        string calldata _counterpartyVersion
     ) external virtual override onlyIBC {
         portId = _portId;
         channelId = _channelId;
@@ -168,15 +169,15 @@ contract PingPong is IBCAppBase {
     }
 
     function onChanCloseInit(
-        string calldata,
-        string calldata
+        string calldata _portId,
+        string calldata _channelId
     ) external virtual override onlyIBC {
         revert("This game is infinite");
     }
 
     function onChanCloseConfirm(
-        string calldata,
-        string calldata
+        string calldata _portId,
+        string calldata _channelId
     ) external virtual override onlyIBC {
         revert("This game is infinite");
     }
diff --git a/evm/contracts/apps/ucs/01-relay/Relay.sol b/evm/contracts/apps/ucs/01-relay/Relay.sol
index 3547e2b581..861e1f7b5d 100644
--- a/evm/contracts/apps/ucs/01-relay/Relay.sol
+++ b/evm/contracts/apps/ucs/01-relay/Relay.sol
@@ -432,10 +432,15 @@ contract UCS01Relay is IBCAppBase {
     }
 
     function onChanOpenAck(
-        string calldata _portId,
-        string calldata _channelId,
+        string calldata portId,
+        string calldata channelId,
+        string calldata counterpartyChannelId,
         string calldata _counterpartyVersion
-    ) external virtual override onlyIBC {}
+    ) external virtual override onlyIBC {
+        // Counterparty channel was empty.
+        counterpartyEndpoints[portId][channelId]
+            .channel_id = counterpartyChannelId;
+    }
 
     function onChanOpenConfirm(
         string calldata _portId,
diff --git a/evm/contracts/core/05-port/IIBCModule.sol b/evm/contracts/core/05-port/IIBCModule.sol
index c51f555b1d..e5aa2679db 100644
--- a/evm/contracts/core/05-port/IIBCModule.sol
+++ b/evm/contracts/core/05-port/IIBCModule.sol
@@ -47,6 +47,7 @@ interface IIBCModule {
     function onChanOpenAck(
         string calldata portId,
         string calldata channelId,
+        string calldata counterpartyChannelId,
         string calldata counterpartyVersion
     ) external;
 
diff --git a/evm/contracts/core/25-handler/IBCChannelHandler.sol b/evm/contracts/core/25-handler/IBCChannelHandler.sol
index ad8717a3bd..180edbcf63 100644
--- a/evm/contracts/core/25-handler/IBCChannelHandler.sol
+++ b/evm/contracts/core/25-handler/IBCChannelHandler.sol
@@ -134,6 +134,7 @@ abstract contract IBCChannelHandler is ModuleManager {
         lookupModuleByPort(msg_.portId).onChanOpenAck(
             msg_.portId,
             msg_.channelId,
+            msg_.counterpartyChannelId,
             msg_.counterpartyVersion
         );
 
diff --git a/evm/contracts/core/DevnetIBCHandlerInit.sol b/evm/contracts/core/DevnetIBCHandlerInit.sol
index 080077efaa..fa179c96c4 100644
--- a/evm/contracts/core/DevnetIBCHandlerInit.sol
+++ b/evm/contracts/core/DevnetIBCHandlerInit.sol
@@ -45,7 +45,12 @@ contract DevnetIBCHandlerInit is IBCHost {
             channel.counterparty,
             channel.version
         );
-        module.onChanOpenAck(portId, channelId, channel.version);
+        module.onChanOpenAck(
+            portId,
+            channelId,
+            channel.counterparty.channel_id,
+            channel.version
+        );
         claimCapability(
             channelCapabilityPath(portId, channelId),
             address(module)
diff --git a/evm/tests/src/MockApp.t.sol b/evm/tests/src/MockApp.t.sol
index 2fcfdeb4f6..5866b4e34a 100644
--- a/evm/tests/src/MockApp.t.sol
+++ b/evm/tests/src/MockApp.t.sol
@@ -52,6 +52,7 @@ contract MockApp is IIBCModule {
     function onChanOpenAck(
         string calldata portId,
         string calldata channelId,
+        string calldata counterpartyChannelId,
         string calldata counterpartyVersion
     ) external virtual override {}
 
diff --git a/evm/tests/src/utils/MockApp.sol b/evm/tests/src/utils/MockApp.sol
index 649ecb79a7..b8c5ae6408 100644
--- a/evm/tests/src/utils/MockApp.sol
+++ b/evm/tests/src/utils/MockApp.sol
@@ -66,6 +66,7 @@ contract MockApp is IIBCModule {
     function onChanOpenAck(
         string calldata portId,
         string calldata channelId,
+        string calldata counterpartyChannelId,
         string calldata counterpartyVersion
     ) external virtual override {
         emit MockChannelOpenAck();