diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 667b22d..4e12e46 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -18,7 +18,7 @@ repos:
         additional_dependencies: [flake8-bugbear]
 
   - repo: https://github.com/pre-commit/mirrors-mypy
-    rev: v0.770
+    rev: v0.780
     hooks:
       - id: mypy
         exclude: ^docs/conf.py
diff --git a/src/black_primer/lib.py b/src/black_primer/lib.py
index afeb072..5c5576e 100644
--- a/src/black_primer/lib.py
+++ b/src/black_primer/lib.py
@@ -59,10 +59,12 @@ async def _gen_check_output(
         raise
 
     if process.returncode != 0:
+        returncode = process.returncode
+        if returncode is None:
+            returncode = 69
+
         cmd_str = " ".join(cmd)
-        raise CalledProcessError(
-            process.returncode, cmd_str, output=stdout, stderr=stderr
-        )
+        raise CalledProcessError(returncode, cmd_str, output=stdout, stderr=stderr)
 
     return (stdout, stderr)