diff --git a/tb/axis_mii_tx.py b/tb/axis_mii_tx.py
index e88b6a1..342d773 100644
--- a/tb/axis_mii_tx.py
+++ b/tb/axis_mii_tx.py
@@ -6,10 +6,10 @@ import random
 import zlib
 
 import cocotb
+from cocotb.binary import BinaryValue
 from cocotb.clock import Clock
 from cocotb.regression import TestFactory
 from cocotb.triggers import ClockCycles, Edge, FallingEdge, First, RisingEdge, Timer
-from cocotb.types import LogicArray
 from cocotb.utils import get_sim_time
 
 from . import axis_replay_buffer
@@ -21,6 +21,7 @@ import os
 skip_slow = not os.environ.get('RUN_SLOW', False)
 
 async def init(mac):
+    mac.clk.value = BinaryValue('Z')
     mac.rst.value = 1
     mac.mii_col.value = 0
     mac.mii_crs.value = 0
diff --git a/tb/axis_replay_buffer.py b/tb/axis_replay_buffer.py
index be9ffd8..2fa740b 100644
--- a/tb/axis_replay_buffer.py
+++ b/tb/axis_replay_buffer.py
@@ -2,6 +2,7 @@
 # Copyright (C) 2022 Sean Anderson <seanga2@gmail.com>
 
 import cocotb
+from cocotb.binary import BinaryValue
 from cocotb.clock import Clock
 from cocotb.regression import TestFactory
 from cocotb.triggers import ClockCycles, FallingEdge, RisingEdge, Timer
@@ -36,6 +37,7 @@ async def send_packet(signals, packet, ratio=1, last_extra=0):
 
 @timeout(30, 'us')
 async def test_replay(buf, in_ratio, out_ratio):
+    buf.clk.value = BinaryValue('Z')
     buf.rst.value = 1
     buf.s_axis_valid.value = 0
     buf.s_axis_last.value = 0