diff --git a/.circleci/config.yml b/.circleci/config.yml
index 6c33d64..131410f 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -23,6 +23,17 @@ jobs:
             sudo pip install nox
             nox -f noxfile.py -s lint
 
+  Type Check:
+      - image: circleci/python:3.7.1
+
+    steps:
+      - checkout
+      - run:
+          command: |
+            sudo pip install virtualenv
+            sudo pip install nox
+            nox -f noxfile.py -s type_check
+
   Release:
     docker:
       - image: circleci/python:3.7.1
@@ -43,6 +54,7 @@ workflows:
     jobs:
       - Unit Test
       - Lint
+      - Type Check
   release:
     jobs:
       - Release:
diff --git a/.gitignore b/.gitignore
index c4f832a..19baadd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -47,6 +47,7 @@ coverage.xml
 *.cover
 .hypothesis/
 .pytest_cache/
+.pytype
 
 # Translations
 *.mo
diff --git a/noxfile.py b/noxfile.py
index 26668e8..52e4160 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -44,3 +44,14 @@ def unit(session, pip_installs):
         'tests',
         *session.posargs
     )
+
+@nox.session
+def type_check(session):
+    """Run type checking using pytype."""
+    session.install('-e', '.[dev]')
+    session.install('pytype')
+    session.run(
+        'pytype',
+        '--python-version=3.6',
+        '--disable=pyi-error',
+        'pybadges')
diff --git a/pybadges/precalculated_text_measurer.py b/pybadges/precalculated_text_measurer.py
index 7f0be9b..4ccd9fd 100644
--- a/pybadges/precalculated_text_measurer.py
+++ b/pybadges/precalculated_text_measurer.py
@@ -20,7 +20,7 @@ Uses a precalculated set of metrics to calculate the string length.
 import io
 import json
 import pkg_resources
-from typing import Mapping, TextIO, Type
+from typing import cast, Mapping, TextIO, Type
 
 from pybadges import text_measurer
 
@@ -80,7 +80,8 @@ class PrecalculatedTextMeasurer(text_measurer.TextMeasurer):
             with pkg_resources.resource_stream(__name__,
                                                'default-widths.json.xz') as f:
                 with lzma.open(f, "rt") as g:
-                    cls._default_cache = PrecalculatedTextMeasurer.from_json(g)
+                    cls._default_cache = PrecalculatedTextMeasurer.from_json(
+                        cast(TextIO, g))
                     return cls._default_cache
         elif pkg_resources.resource_exists(__name__, 'default-widths.json'):
             with pkg_resources.resource_stream(__name__,