diff --git a/MANIFEST.in b/MANIFEST.in
index 0bfae58e3..7331f6d30 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -15,7 +15,7 @@ recursive-include demo *
 include cythonize.dat
 
 # Add build and testing tools
-include tox.ini
+include tox.ini pytest.ini
 recursive-include util *
 
 # Exclude what we don't want to include
diff --git a/pywt/conftest.py b/pywt/conftest.py
new file mode 100644
index 000000000..da8ae6455
--- /dev/null
+++ b/pywt/conftest.py
@@ -0,0 +1,6 @@
+import pytest
+
+
+def pytest_configure(config):
+    config.addinivalue_line("markers",
+                            "slow: Tests that are slow.")