diff --git a/doc/spec/dir-spec.txt b/doc/spec/dir-spec.txt
index c2b62b3cab..c8a47b7fc9 100644
--- a/doc/spec/dir-spec.txt
+++ b/doc/spec/dir-spec.txt
@@ -654,7 +654,7 @@ $Id$
 
 2.3. Nonterminals in router descriptors
 
-   nickname ::= between 1 and 19 alphanumeric characters ([A-Za-z0-0]),
+   nickname ::= between 1 and 19 alphanumeric characters ([A-Za-z0-9]),
       case-insensitive.
    hexdigest ::= a '$', followed by 40 hexadecimal characters
       ([A-Fa-f0-9]). [Represents a server by the digest of its identity