diff --git a/lib/matplotlib/tests/test_font_manager.py b/lib/matplotlib/tests/test_font_manager.py
index 16b5551193cc..b4de12d3b571 100644
--- a/lib/matplotlib/tests/test_font_manager.py
+++ b/lib/matplotlib/tests/test_font_manager.py
@@ -340,7 +340,7 @@ def inner():
         with BytesIO() as out:
             with warnings.catch_warnings():
                 warnings.filterwarnings('ignore')
-                fig.savefig(out, format='png')
+                fig.savefig(out, format='raw')
 
     inner()