diff --git a/conftest.py b/conftest.py
index b2065532..425740dd 100644
--- a/conftest.py
+++ b/conftest.py
@@ -1,4 +1,25 @@
+import pytest
+
+import cssutils
+
+
 collect_ignore = [
     'cssutils/_fetchgae.py',
     'tools',
 ]
+
+
+@pytest.fixture(autouse=True)
+def hermetic_profiles():
+    """
+    Ensure that tests are hermetic w.r.t. profiles.
+    """
+    before = list(cssutils.profile.profiles)
+    yield
+    assert before == cssutils.profile.profiles
+
+
+@pytest.fixture
+def saved_profiles(monkeypatch):
+    profiles = cssutils.profiles.Profiles(log=cssutils.log)
+    monkeypatch.setattr(cssutils, 'profile', profiles)
diff --git a/cssutils/tests/test_profiles.py b/cssutils/tests/test_profiles.py
index c9976c59..1348bc00 100644
--- a/cssutils/tests/test_profiles.py
+++ b/cssutils/tests/test_profiles.py
@@ -78,6 +78,7 @@ def check(*results):
         # restore
         cssutils.profile = saved
 
+    @pytest.mark.usefixtures('saved_profiles')
     def test_addProfile(self):
         "Profiles.addProfile with custom validation function"
         # unknown profile
diff --git a/examples/website.py b/examples/website.py
index f41c1618..0c74d1be 100644
--- a/examples/website.py
+++ b/examples/website.py
@@ -11,8 +11,7 @@ def profile():
     """
     >>> sheet = cssutils.parseString('x { -test-custommacro: x }')
 
-    The following fails in a full suite test run due to non-hermetic tests.
-    >>> print(sheet.cssRules[0].style.getProperties()[0].valid)  # doctest: +SKIP
+    >>> print(sheet.cssRules[0].style.getProperties()[0].valid)
     False
     >>> M1 = {
     ...      'testvalue': 'x'
@@ -24,6 +23,7 @@ def profile():
     ...    # custom validation function
     ...    '-test-funcval': lambda v: int(v) > 0
     ...      }
+    >>> profiles = getfixture('saved_profiles')  # keep test hermetic
     >>> cssutils.profile.addProfile('test', P1, M1)
     >>> sheet = cssutils.parseString('x { -test-custommacro: x }')
     >>> print(sheet.cssRules[0].style.getProperties()[0].valid)