diff --git a/.travis.yml b/.travis.yml
index 4c34343..9e48e67 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,6 +15,8 @@ matrix:
       env: TOXENV=codestyle
     - python: 3.8
       env: TOXENV=docstyle
+    - python: 3.8
+      env: TOXENV=mypy
     - python: 3.8
       env: TOXENV=py38
     - python: 3.7
@@ -34,6 +36,9 @@ matrix:
     - python: 3.8
       arch: ppc64le
       env: TOXENV=docstyle
+    - python: 3.8
+      arch: ppc64le
+      env: TOXENV=mypy
     - python: 3.8
       arch: ppc64le
       env: TOXENV=py38
@@ -55,12 +60,6 @@ matrix:
     - arch: ppc64le
       python: pypy3
 
-before_install:
-  - | 
-   if [[ "$TRAVIS_CPU_ARCH" == "ppc64le" ]]; then
-     sudo chown -Rv $USER:$GROUP ~/.cache/pip/wheels
-   fi
-
 install: 
   - pip install tox
   - if [[ "$TRAVIS_CPU_ARCH" == "ppc64le" ]]; then pip install pytest; pip install astropy; fi
diff --git a/MANIFEST.in b/MANIFEST.in
index c30aef0..94204e2 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,3 +1,4 @@
 include README.rst
 include LICENSE.txt
-include *jdcal.py
+include src/jdcal/*.py
+include src/jdcal/py.typed
diff --git a/setup.py b/setup.py
index eade07b..2520dd5 100644
--- a/setup.py
+++ b/setup.py
@@ -1,16 +1,16 @@
 #!/usr/bin/env python
 
-from setuptools import setup
+from setuptools import setup, find_packages
 
-import jdcal
-
-version = jdcal.__version__
 
 long_description = open("README.rst").read()
 
+with open("src/jdcal/version.py") as f:
+    exec(f.read())
+
 setup(
     name="jdcal",
-    version=version,
+    version=__version__,
     description="Julian dates from proleptic Gregorian and Julian calendars.",
     long_description=long_description,
     license='BSD',
@@ -35,5 +35,9 @@
         'Programming Language :: Python :: Implementation :: CPython',
         'Programming Language :: Python :: Implementation :: PyPy',
     ],
-    py_modules=["jdcal"]
+    # py_modules=["jdcal"],
+    packages=find_packages("src"),
+    package_dir={"": "src"},
+    install_requires=["typing;python_version<'3.5'"],
+    include_package_data=True,
 )
diff --git a/src/jdcal/__init__.py b/src/jdcal/__init__.py
new file mode 100644
index 0000000..2667a23
--- /dev/null
+++ b/src/jdcal/__init__.py
@@ -0,0 +1,14 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# see https://mypy.readthedocs.io/en/latest/config_file.html#confval-implicit_reexport
+from .version import __version__ as __version__
+from .jdcal import (
+    MJD_0 as MJD_0,
+    MJD_JD2000 as MJD_JD2000,
+    is_leap as is_leap,
+    gcal2jd as gcal2jd,
+    jd2gcal as jd2gcal,
+    jcal2jd as jcal2jd,
+    jd2jcal as jd2jcal,
+)
diff --git a/jdcal.py b/src/jdcal/jdcal.py
similarity index 96%
rename from jdcal.py
rename to src/jdcal/jdcal.py
index cb1661c..4d3ac37 100644
--- a/jdcal.py
+++ b/src/jdcal/jdcal.py
@@ -41,14 +41,14 @@
 from __future__ import division
 from __future__ import print_function
 import math
+from typing import Tuple
 
-__version__ = "1.4.1"
 
 MJD_0 = 2400000.5
 MJD_JD2000 = 51544.5
 
 
-def is_leap(year):
+def is_leap(year):  # type: (int) -> int
     """Leap year or not in the Gregorian calendar."""
     x = year % 4
     y = year % 100
@@ -59,7 +59,7 @@ def is_leap(year):
     return not x and (y or not z)
 
 
-def gcal2jd(year, month, day):
+def gcal2jd(year, month, day):  # type: (int, int, int) -> Tuple[float, float]
     """Gregorian calendar date to Julian date.
 
     The input and output are for the proleptic Gregorian calendar,
@@ -179,7 +179,7 @@ def gcal2jd(year, month, day):
     day = int(day)
 
     a = int((month - 14) / 12.0)
-    jd = int((1461 * (year + 4800 + a)) / 4.0)
+    jd = int((1461 * (year + 4800 + a)) / 4.0)  # type: float
     jd += int((367 * (month - 2 - 12 * a)) / 12.0)
     x = int((year + 4900 + a) / 100.0)
     jd -= int((3 * x) / 4.0)
@@ -190,7 +190,7 @@ def gcal2jd(year, month, day):
     return MJD_0, jd
 
 
-def jd2gcal(jd1, jd2):
+def jd2gcal(jd1, jd2):  # type: (float, float) -> Tuple[int, int, int, float]
     """Julian date to Gregorian calendar date and time of day.
 
     The input and output are for the proleptic Gregorian calendar,
@@ -289,7 +289,7 @@ def jd2gcal(jd1, jd2):
     return int(year), int(month), int(day), f
 
 
-def jcal2jd(year, month, day):
+def jcal2jd(year, month, day):  # type: (int, int, int) -> Tuple[float, float]
     """Julian calendar date to Julian date.
 
     The input and output are for the proleptic Julian calendar,
@@ -344,7 +344,7 @@ def jcal2jd(year, month, day):
     month = int(month)
     day = int(day)
 
-    jd = 367 * year
+    jd = 367 * year  # type: float
     x = int((month - 9) / 7.0)
     jd -= int((7 * (year + 5001 + x)) / 4.0)
     jd += int((275 * month) / 9.0)
@@ -356,7 +356,7 @@ def jcal2jd(year, month, day):
     return MJD_0, jd
 
 
-def jd2jcal(jd1, jd2):
+def jd2jcal(jd1, jd2):  # type: (float, float) -> Tuple[int, int, int, float]
     """Julian calendar date for the given Julian date.
 
     The input and output are for the proleptic Julian calendar,
diff --git a/src/jdcal/py.typed b/src/jdcal/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/src/jdcal/version.py b/src/jdcal/version.py
new file mode 100644
index 0000000..afbd696
--- /dev/null
+++ b/src/jdcal/version.py
@@ -0,0 +1,4 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+__version__ = "1.4.1"
diff --git a/test_jdcal.py b/tests/test_jdcal.py
similarity index 100%
rename from test_jdcal.py
rename to tests/test_jdcal.py
diff --git a/tox.ini b/tox.ini
index 9e4d1cf..ab3ab32 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 project = jdcal
-envlist = py{27,34,35,36,37,38,py,py3}, codestyle, docstyle
+envlist = py{27,34,35,36,37,38,py,py3}, codestyle, docstyle, mypy
 
 [testenv]
 deps = pytest
@@ -13,8 +13,12 @@ deps =
 
 [testenv:codestyle]
 deps = pycodestyle
-commands = pycodestyle --ignore=E722,E501 jdcal.py test_jdcal.py
+commands = pycodestyle --ignore=E722,E501 src/jdcal/jdcal.py tests/test_jdcal.py
 
 [testenv:docstyle]
 deps = pydocstyle
-commands = pydocstyle jdcal.py test_jdcal.py
+commands = pydocstyle src/jdcal/jdcal.py 
+
+[testenv:mypy]
+deps = mypy
+commands = mypy --strict src/jdcal/jdcal.py