diff --git a/changelog/4770.bugfix.rst b/changelog/4770.bugfix.rst
new file mode 100644
index 000000000..8fbb99e1b
--- /dev/null
+++ b/changelog/4770.bugfix.rst
@@ -0,0 +1 @@
+``more_itertools`` is now constrained to <6.0.0 when required for Python 2.7 compatibility.
diff --git a/setup.py b/setup.py
index 696fc4028..b286a4f20 100644
--- a/setup.py
+++ b/setup.py
@@ -10,7 +10,8 @@ INSTALL_REQUIRES = [
     "six>=1.10.0",
     "setuptools",
     "attrs>=17.4.0",
-    "more-itertools>=4.0.0",
+    'more-itertools>=4.0.0,<6.0.0;python_version<="2.7"',
+    'more-itertools>=4.0.0;python_version>"2.7"',
     "atomicwrites>=1.0",
     'funcsigs;python_version<"3.0"',
     'pathlib2>=2.2.0;python_version<"3.6"',