diff --git a/setup.py b/setup.py
index <HASH>..<HASH> 100644
--- a/setup.py
+++ b/setup.py
@@ -73,6 +73,7 @@ setup(
         "ukpostcodeparser>=1.1.1",
         "mock",
         "pytest>=3.8.0,<3.9",
+        "more-itertools<6.0.0",
     ],
     extras_require={
         ':python_version=="2.7"': [
Pin more-itertools to a version compatible with py<I> (#<I>)