diff --git a/lib/matplotlib/tests/test_agg_filter.py b/lib/matplotlib/tests/test_agg_filter.py
index 419071b1a453..913034636603 100644
--- a/lib/matplotlib/tests/test_agg_filter.py
+++ b/lib/matplotlib/tests/test_agg_filter.py
@@ -4,7 +4,8 @@
 from matplotlib.testing.decorators import image_comparison
 
 
-@image_comparison(baseline_images=['agg_filter_alpha'])
+@image_comparison(baseline_images=['agg_filter_alpha'],
+                  extensions=['png', 'pdf'])
 def test_agg_filter_alpha():
     ax = plt.axes()
     x, y = np.mgrid[0:7, 0:8]