diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
index 31f755e4375a..25de00219dc0 100644
--- a/lib/matplotlib/rcsetup.py
+++ b/lib/matplotlib/rcsetup.py
@@ -471,7 +471,7 @@ def validate_fontweight(s):
     try:
         return int(s)
     except (ValueError, TypeError):
-        raise ValueError(f'{s} is not a valid font weight. %s')
+        raise ValueError(f'{s} is not a valid font weight.')
 
 
 def validate_font_properties(s):