diff --git a/src/stacky/stacky.py b/src/stacky/stacky.py
index 26c1a0b..2e5a1f1 100755
--- a/src/stacky/stacky.py
+++ b/src/stacky/stacky.py
@@ -30,7 +30,7 @@
 import subprocess
 import sys
 from argparse import ArgumentParser
-from typing import List, Optional, Tuple
+from typing import List, Optional
 
 import asciitree
 import colors
@@ -246,7 +246,11 @@ def get_pr_info(branch, *, full=False):
     infos = {info["id"]: info for info in infos}
     open_prs = [info for info in infos.values() if info["state"] == "OPEN"]
     if len(open_prs) > 1:
-        die("Branch {} has more than one open PR: {}", branch, ", ".join(open_prs))
+        die(
+            "Branch {} has more than one open PR: {}",
+            branch,
+            ", ".join([str(pr) for pr in open_prs]),
+        )
     return infos, open_prs[0] if open_prs else None
 
 
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..71d17ce
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,5 @@
+[flake8]
+ignore = D203, E501, W503, E203
+exclude = .git,__pycache__,docs/source/conf.py,old,build,dist
+max-complexity = 10
+max-line-length = 120