diff --git a/src/ecdsa/_compat.py b/src/ecdsa/_compat.py
index f409a1a2..4558e33a 100644
--- a/src/ecdsa/_compat.py
+++ b/src/ecdsa/_compat.py
@@ -127,7 +127,7 @@ def int_to_bytes(val, length=None, byteorder="big"):
         if length is None:
             length = byte_length(val)
         # for gmpy we need to convert back to native int
-        if type(val) != int:
+        if not isinstance(val, int):
             val = int(val)
         return bytearray(val.to_bytes(length=length, byteorder=byteorder))
 
diff --git a/tox.ini b/tox.ini
index c9b07c9a..ea01c4b4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -104,7 +104,7 @@ commands = {envpython} speed.py
 basepython = python3
 deps =
      black==22.3.0
-     flake8
+     flake8==6.1.0
 commands =
          flake8 setup.py speed.py src
          black --check --line-length 79 .