diff --git a/kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt b/kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt
index 15d61c19..04f18f8d 100644
--- a/kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt
+++ b/kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt
@@ -169,6 +169,11 @@ public open class Server(
             }
         }
 
+        // Register cleanup handler to remove session from list when it closes
+        session.onClose {
+            logger.debug { "Removing closed session from active sessions list" }
+            sessions.update { list -> list - session }
+        }
         logger.debug { "Server session connecting to transport" }
         session.connect(transport)
         logger.debug { "Server session successfully connected to transport" }