diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/InternalHttpAsyncClient.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/InternalHttpAsyncClient.java
index 98e5b2e8b..013e687fb 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/InternalHttpAsyncClient.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/InternalHttpAsyncClient.java
@@ -150,6 +150,11 @@ class InternalHttpAsyncClient extends AbstractHttpAsyncClientBase {
             log.debug(exchangeId + ": preparing request execution");
         }
 
+        //TODO remove when fixed in HttpCore
+        if (route.isTunnelled()) {
+            throw new HttpException("HTTP tunneling not supported");
+        }
+
         setupContext(clientContext);
 
         final AsyncExecChain.Scope scope = new AsyncExecChain.Scope(exchangeId, route, request, clientContext, execRuntime);