diff --git a/gateware/sampler/circular_buffer.py b/gateware/sampler/circular_buffer.py
index 0012697..d1b5f1f 100644
--- a/gateware/sampler/circular_buffer.py
+++ b/gateware/sampler/circular_buffer.py
@@ -111,7 +111,7 @@ class CircularBuffer(Module):
 
 
 def testbench():
-    dut = CircularBuffer(9, 24)
+    dut = CircularBuffer(9, 24, with_wb=False)
     def test_fn():
         assert (yield dut.len) == 0
         assert (yield dut.wr_ready) == 1