diff --git a/packages/google-cloud-vision/nox.py b/packages/google-cloud-vision/nox.py
index d5d3f3412ef7..8761fa6fccd6 100644
--- a/packages/google-cloud-vision/nox.py
+++ b/packages/google-cloud-vision/nox.py
@@ -46,7 +46,7 @@ def system_tests(session, python_version):
 
     # Sanity check: Only run system tests if the environment variable is set.
     if not os.environ.get('GOOGLE_APPLICATION_CREDENTIALS', ''):
-        return
+        session.skip('Credentials must be set via environment variable.')
 
     # Run unit tests against all supported versions of Python.
     session.interpreter = 'python{}'.format(python_version)
@@ -67,7 +67,7 @@ def system_tests_manual_layer(session, python_version):
 
     # Sanity check: Only run system tests if the environment variable is set.
     if not os.environ.get('GOOGLE_APPLICATION_CREDENTIALS', ''):
-        return
+        session.skip('Credentials must be set via environment variable.')
 
     # Run unit tests against all supported versions of Python.
     session.interpreter = 'python{}'.format(python_version)