diff --git a/marshal.c b/marshal.c
index 2a61b78448..808aa0f9af 100644
--- a/marshal.c
+++ b/marshal.c
@@ -864,7 +864,7 @@ clear_dump_arg(struct dump_arg *arg)
 
 /*
  * call-seq:
- *      dump( obj [, anIO] , limit=--1 ) -> anIO
+ *      dump( obj [, anIO] , limit=-1 ) -> anIO
  *
  * Serializes obj and all descendant objects. If anIO is
  * specified, the serialized data will be written to it, otherwise the