diff --git a/tb/test_axis_cobs_decode.py b/tb/test_axis_cobs_decode.py
index d8ef20f4..4487a30c 100755
--- a/tb/test_axis_cobs_decode.py
+++ b/tb/test_axis_cobs_decode.py
@@ -260,7 +260,7 @@ def bench():
 
         # testbench stimulus
 
-        for payload_len in list(range(1,33))+list(range(252,261))+[512,1024]:
+        for payload_len in list(range(1,33))+list(range(253,259))+[512]:
             gen = prbs31()
             for block in [bytearray([0]*payload_len),
                         bytearray([k%255+1 for k in range(payload_len)]),
diff --git a/tb/test_axis_cobs_encode.py b/tb/test_axis_cobs_encode.py
index 6422de2a..e3efef76 100755
--- a/tb/test_axis_cobs_encode.py
+++ b/tb/test_axis_cobs_encode.py
@@ -261,7 +261,7 @@ def bench():
 
         # testbench stimulus
 
-        for payload_len in list(range(1,33))+list(range(252,261))+[512,1024]:
+        for payload_len in list(range(1,33))+list(range(253,259))+[512]:
             gen = prbs31()
             for block in [bytearray([0]*payload_len),
                         bytearray([k%255+1 for k in range(payload_len)]),
diff --git a/tb/test_axis_cobs_encode_zero_frame.py b/tb/test_axis_cobs_encode_zero_frame.py
index b4fe9e8b..a7171f8f 100755
--- a/tb/test_axis_cobs_encode_zero_frame.py
+++ b/tb/test_axis_cobs_encode_zero_frame.py
@@ -261,7 +261,7 @@ def bench():
 
         # testbench stimulus
 
-        for payload_len in list(range(1,33))+list(range(252,261))+[512,1024]:
+        for payload_len in list(range(1,33))+list(range(253,259))+[512]:
             gen = prbs31()
             for block in [bytearray([0]*payload_len),
                         bytearray([k%255+1 for k in range(payload_len)]),