diff --git a/tb/arp_ep.py b/tb/arp_ep.py
index d6b29fbf..8c296bf1 100644
--- a/tb/arp_ep.py
+++ b/tb/arp_ep.py
@@ -153,18 +153,18 @@ class ARPFrame(object):
 def ARPFrameSource(clk, rst,
                    frame_valid=None,
                    frame_ready=None,
-                   eth_dest_mac=None,
-                   eth_src_mac=None,
-                   eth_type=None,
-                   arp_htype=None,
-                   arp_ptype=None,
-                   arp_hlen=Signal(intbv(0)[8:]),
-                   arp_plen=Signal(intbv(0)[8:]),
-                   arp_oper=None,
-                   arp_sha=None,
-                   arp_spa=None,
-                   arp_tha=None,
-                   arp_tpa=None,
+                   eth_dest_mac=Signal(intbv(0)[48:]),
+                   eth_src_mac=Signal(intbv(0)[48:]),
+                   eth_type=Signal(intbv(0)[16:]),
+                   arp_htype=Signal(intbv(0)[16:]),
+                   arp_ptype=Signal(intbv(0)[16:]),
+                   arp_hlen=Signal(intbv(6)[8:]),
+                   arp_plen=Signal(intbv(4)[8:]),
+                   arp_oper=Signal(intbv(0)[16:]),
+                   arp_sha=Signal(intbv(0)[48:]),
+                   arp_spa=Signal(intbv(0)[32:]),
+                   arp_tha=Signal(intbv(0)[48:]),
+                   arp_tpa=Signal(intbv(0)[32:]),
                    fifo=None,
                    pause=0,
                    name=None):
@@ -217,18 +217,18 @@ def ARPFrameSource(clk, rst,
 def ARPFrameSink(clk, rst,
                  frame_valid=None,
                  frame_ready=None,
-                 eth_dest_mac=None,
-                 eth_src_mac=None,
-                 eth_type=None,
-                 arp_htype=None,
-                 arp_ptype=None,
-                 arp_hlen=None,
-                 arp_plen=None,
-                 arp_oper=None,
-                 arp_sha=None,
-                 arp_spa=None,
-                 arp_tha=None,
-                 arp_tpa=None,
+                 eth_dest_mac=Signal(intbv(0)[48:]),
+                 eth_src_mac=Signal(intbv(0)[48:]),
+                 eth_type=Signal(intbv(0)[16:]),
+                 arp_htype=Signal(intbv(0)[16:]),
+                 arp_ptype=Signal(intbv(0)[16:]),
+                 arp_hlen=Signal(intbv(6)[8:]),
+                 arp_plen=Signal(intbv(4)[8:]),
+                 arp_oper=Signal(intbv(0)[16:]),
+                 arp_sha=Signal(intbv(0)[48:]),
+                 arp_spa=Signal(intbv(0)[32:]),
+                 arp_tha=Signal(intbv(0)[48:]),
+                 arp_tpa=Signal(intbv(0)[32:]),
                  fifo=None,
                  pause=0,
                  name=None):
diff --git a/tb/eth_ep.py b/tb/eth_ep.py
index a71086f4..4fd9fcdb 100644
--- a/tb/eth_ep.py
+++ b/tb/eth_ep.py
@@ -89,9 +89,9 @@ class EthFrame(object):
 def EthFrameSource(clk, rst,
                    eth_hdr_valid=None,
                    eth_hdr_ready=None,
-                   eth_dest_mac=None,
-                   eth_src_mac=None,
-                   eth_type=None,
+                   eth_dest_mac=Signal(intbv(0)[48:]),
+                   eth_src_mac=Signal(intbv(0)[48:]),
+                   eth_type=Signal(intbv(0)[16:]),
                    eth_payload_tdata=None,
                    eth_payload_tkeep=Signal(bool(True)),
                    eth_payload_tvalid=Signal(bool(False)),
@@ -157,9 +157,9 @@ def EthFrameSource(clk, rst,
 def EthFrameSink(clk, rst,
                  eth_hdr_valid=None,
                  eth_hdr_ready=None,
-                 eth_dest_mac=None,
-                 eth_src_mac=None,
-                 eth_type=None,
+                 eth_dest_mac=Signal(intbv(0)[48:]),
+                 eth_src_mac=Signal(intbv(0)[48:]),
+                 eth_type=Signal(intbv(0)[16:]),
                  eth_payload_tdata=None,
                  eth_payload_tkeep=Signal(bool(True)),
                  eth_payload_tvalid=Signal(bool(True)),