diff --git a/string.c b/string.c
index c00fa3cd5c..4b10503e8f 100644
--- a/string.c
+++ b/string.c
@@ -5468,8 +5468,6 @@ rb_str_setter(VALUE val, ID id, VALUE *var)
  *     str.force_encoding(encoding)   => str
  *
  *  Changes the encoding to +encoding+ and returns self.
- *
- *  If nil is given as +encoding+, "ASCII-8BIT" is used.
  */
 
 static VALUE