diff --git a/setup.py b/setup.py
index b6d4ce7..4d27af6 100644
--- a/setup.py
+++ b/setup.py
@@ -25,9 +25,12 @@
     ],
     extras_require={
         'dev': [
+            'mypy',
             'pytest',
             'pylint',
             'pycodestyle',
         ],
     },
+
+    package_data=dict(unicodeit=['py.typed'])
 )
diff --git a/unicodeit/py.typed b/unicodeit/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/unicodeit/replace.py b/unicodeit/replace.py
index 1c7138c..405ed91 100644
--- a/unicodeit/replace.py
+++ b/unicodeit/replace.py
@@ -4,7 +4,7 @@
 from .data import REPLACEMENTS, COMBININGMARKS, SUBSUPERSCRIPTS
 
 
-def replace(f: str):
+def replace(f: str) -> str:
     # Catch cases like \not\subset and \not\in and convert them to
     # use the combining character slash as in \slash{\subset}
     f = re.sub(r'\\not(\\[A-z]+)', r'\\slash{\1}', f)