diff --git a/gnu/usr.bin/man/lib/util.c b/gnu/usr.bin/man/lib/util.c
index 14a6cb912d6..6db023b7368 100644
--- a/gnu/usr.bin/man/lib/util.c
+++ b/gnu/usr.bin/man/lib/util.c
@@ -59,7 +59,8 @@ downcase (s)
   while ((c = *s) != '\0')
     {
       if (isalpha (c))
-	*s++ = tolower (c);
+	*s = tolower (c);
+      s++;
     }
 }