diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
index e5a4f21dcfef..c2907cff6e9d 100644
--- a/lib/matplotlib/font_manager.py
+++ b/lib/matplotlib/font_manager.py
@@ -1352,7 +1352,7 @@ def is_opentype_cff_font(filename):
         if result is None:
             with open(filename, 'rb') as fd:
                 tag = fd.read(4)
-            result = (tag == 'OTTO')
+            result = (tag == b'OTTO')
             _is_opentype_cff_font_cache[filename] = result
         return result
     return False