diff --git a/tests/test_connection.py b/tests/test_connection.py
index 9b152bb44..1118bea51 100644
--- a/tests/test_connection.py
+++ b/tests/test_connection.py
@@ -4846,6 +4846,41 @@ def test_no_delay(node_factory):
     assert end < start + 100 * 0.5
 
 
+@unittest.skipIf(os.getenv('TEST_BENCH', '0') == '0', "For profiling")
+def test_bench(node_factory):
+    """Is our Nagle disabling for critical messages working?"""
+    l1, l2 = node_factory.get_nodes(2, opts={'start': False,
+                                             'commit-time': 0})
+
+    # memleak detection plays havoc with profiles.
+    del l1.daemon.env["LIGHTNINGD_DEV_MEMLEAK"]
+    del l2.daemon.env["LIGHTNINGD_DEV_MEMLEAK"]
+
+    l1.start()
+    l2.start()
+    node_factory.join_nodes([l1, l2])
+
+    scid = only_one(l1.rpc.listpeerchannels()['channels'])['short_channel_id']
+    routestep = {
+        'amount_msat': 100,
+        'id': l2.info['id'],
+        'delay': 5,
+        'channel': scid
+    }
+
+    start = time.time()
+    # If we were stupid enough to leave Nagle enabled, this would add 200ms
+    # seconds delays each way!
+    for _ in range(1000):
+        phash = random.randbytes(32).hex()
+        l1.rpc.sendpay([routestep], phash)
+        with pytest.raises(RpcError, match="WIRE_INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS"):
+            l1.rpc.waitsendpay(phash)
+    end = time.time()
+    duration = end - start
+    assert duration == 0
+
+
 def test_listpeerchannels_by_scid(node_factory):
     l1, l2, l3 = node_factory.line_graph(3, announce_channels=False)