diff --git a/lib/adapter/http.js b/lib/adapter/http.js
index <HASH>..<HASH> 100644
--- a/lib/adapter/http.js
+++ b/lib/adapter/http.js
@@ -50,6 +50,14 @@ function createRequestResponseHandler(params) {
         return;
       }
       var connection = connectionPool.get();
+      if (!connection) {
+        // When the cluster members are changing, we cannot get
+        // actual connection for a member, so retry later.
+        setTimeout(function() {
+          processRequest();
+        }, CONNECTION_RETRY_INTERVAL);
+        return;
+      }
       var wrappedConnection = new wrapper.DroongaProtocolConnectionWrapper(connection, callback, options);
       if (definition.onRequest) {
         try {
Don't create new connection while updating