diff --git a/Doc/library/string.rst b/Doc/library/string.rst
index cc05a7d..d3789d4 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -565,7 +565,7 @@
 Helper functions
 ----------------
 
-.. function:: capwords(s[, sep])
+.. function:: capwords(s, sep=' ')
 
    Split the argument into words using :meth:`str.split`, capitalize each word
    using :meth:`str.capitalize`, and join the capitalized words using