diff --git a/pyproject.toml b/pyproject.toml
index 869afb88..774860c8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,6 +28,7 @@ classifiers = [
     "Topic :: Software Development :: Quality Assurance",
     "Topic :: Software Development :: Testing",
 ]
+include = ["ward/py.typed"]
 
 [tool.poetry.dependencies]
 python = "^3.6.1"
diff --git a/ward/py.typed b/ward/py.typed
new file mode 100644
index 00000000..7632ecf7
--- /dev/null
+++ b/ward/py.typed
@@ -0,0 +1 @@
+# Marker file for PEP 561