diff --git a/src/modules/drouting/README b/src/modules/drouting/README
index 8e45c5ecf1..b07550a069 100644
@@ -295,7 +295,8 @@ Chapter 1. Admin Guide
Each user must be member of only one routing group. It must be
specified in user's profile.
b. prefix column
- Destination URI must start with prefix value to match the rule.
+ Destination URI must start with prefix value to match the rule. The
+ prefix value can contain only digits (0..9), '+', '*' or '#'.
c. time rec column
A date-time expression that defines the time recurrence to match
for current rule. Time recurrences are based closely on the