diff --git a/src/cluster/websocket/WebSocket.cc b/src/cluster/websocket/WebSocket.cc
index 428101fedf..c70fd1c728 100644
--- a/src/cluster/websocket/WebSocket.cc
+++ b/src/cluster/websocket/WebSocket.cc
@@ -394,6 +394,14 @@ void WebSocketEventDispatcher::HandleSubscriptions(WebSocketClientEntry& entry,
 
     entry.wsc->SetSubscriptions(subscriptions);
 
+    // Short-circuit setting up subscriptions and directly reply with
+    // an ack if the client didn't request any topic subscriptions.
+    if ( subscriptions.empty() ) {
+        assert(entry.wsc->AllSubscriptionsActive());
+        HandleSubscriptionsActive(entry);
+        return;
+    }
+
     auto cb = [this, id = entry.id, wsc = entry.wsc](const std::string& topic,
                                                      const Backend::SubscriptionCallbackInfo& info) {
         if ( info.status == Backend::CallbackStatus::Error ) {
diff --git a/testing/btest/Baseline/cluster.websocket.no-subscriptions/..client..stderr b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..client..stderr
new file mode 100644
index 0000000000..49d861c74c
--- /dev/null
+++ b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..client..stderr
@@ -0,0 +1 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
diff --git a/testing/btest/Baseline/cluster.websocket.no-subscriptions/..client..stdout b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..client..stdout
new file mode 100644
index 0000000000..49d861c74c
--- /dev/null
+++ b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..client..stdout
@@ -0,0 +1 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
diff --git a/testing/btest/Baseline/cluster.websocket.no-subscriptions/..manager..stderr b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..manager..stderr
new file mode 100644
index 0000000000..e3f6131b1d
--- /dev/null
+++ b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..manager..stderr
@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+received termination signal
diff --git a/testing/btest/Baseline/cluster.websocket.no-subscriptions/..manager..stdout b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..manager..stdout
new file mode 100644
index 0000000000..bb622d5ce2
--- /dev/null
+++ b/testing/btest/Baseline/cluster.websocket.no-subscriptions/..manager..stdout
@@ -0,0 +1,3 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+Cluster::websocket_client_added, []
+got ping, 42
diff --git a/testing/btest/cluster/websocket/no-subscriptions.zeek b/testing/btest/cluster/websocket/no-subscriptions.zeek
new file mode 100644
index 0000000000..50405ea74b
--- /dev/null
+++ b/testing/btest/cluster/websocket/no-subscriptions.zeek
@@ -0,0 +1,67 @@
+# @TEST-DOC: Regression test: A WebSocket client sending no subscriptions wasn't receiving back an ack.
+#
+# @TEST-REQUIRES: have-zeromq
+# @TEST-REQUIRES: python3 -c 'import websockets.sync'
+#
+# @TEST-GROUP: cluster-zeromq
+#
+# @TEST-PORT: XPUB_PORT
+# @TEST-PORT: XSUB_PORT
+# @TEST-PORT: LOG_PULL_PORT
+# @TEST-PORT: WEBSOCKET_PORT
+#
+# @TEST-EXEC: cp $FILES/zeromq/cluster-layout-simple.zeek cluster-layout.zeek
+# @TEST-EXEC: cp $FILES/zeromq/test-bootstrap.zeek zeromq-test-bootstrap.zeek
+# @TEST-EXEC: cp $FILES/ws/wstest.py .
+#
+# @TEST-EXEC: zeek -b --parse-only manager.zeek
+# @TEST-EXEC: python3 -m py_compile client.py
+#
+# @TEST-EXEC: btest-bg-run manager "ZEEKPATH=$ZEEKPATH:.. && CLUSTER_NODE=manager zeek -b ../manager.zeek"
+# @TEST-EXEC: btest-bg-run client "python3 ../client.py"
+#
+# @TEST-EXEC: btest-bg-wait 30
+# @TEST-EXEC: btest-diff ./manager/.stdout
+# @TEST-EXEC: btest-diff ./manager/.stderr
+# @TEST-EXEC: btest-diff ./client/.stdout
+# @TEST-EXEC: btest-diff ./client/.stderr
+
+# @TEST-START-FILE manager.zeek
+@load ./zeromq-test-bootstrap
+redef exit_only_after_terminate = T;
+
+global expected_ping_count = 100;
+global ping_count = 0;
+
+event zeek_init()
+	{
+	Cluster::subscribe("/test/pings");
+	Cluster::listen_websocket([$listen_host="127.0.0.1", $listen_port=to_port(getenv("WEBSOCKET_PORT"))]);
+	}
+
+event ping(c: count) &is_used
+	{
+	print "got ping", c;
+	terminate();
+	}
+
+event Cluster::websocket_client_added(info: Cluster::EndpointInfo, subscriptions: string_vec)
+	{
+	print "Cluster::websocket_client_added", subscriptions;
+	}
+# @TEST-END-FILE
+
+
+# @TEST-START-FILE client.py
+import wstest
+
+def run(ws_url):
+    with wstest.connect("ws1", ws_url) as tc:
+        tc.send_json([])  # Send no subscriptions
+        ack = tc.recv_json()
+        assert ack.get("type") == "ack", f"{ack}"
+        tc.send_json(wstest.build_event_v1("/test/pings/", "ping", [42]))
+
+if __name__ == "__main__":
+    wstest.main(run, wstest.WS4_URL_V1)
+# @TEST-END-FILE