diff --git a/api/v1/auth.go b/api/v1/auth.go
index f27b36cc..52102605 100644
--- a/api/v1/auth.go
+++ b/api/v1/auth.go
@@ -22,7 +22,7 @@ import (
 )
 
 var (
-	usernameMatcher = regexp.MustCompile("^[a-z]([a-z0-9-]{1,30}[a-z0-9])?$")
+	usernameMatcher = regexp.MustCompile("^[a-z0-9]([a-z0-9-]{1,30}[a-z0-9])$")
 )
 
 type SignIn struct {
diff --git a/api/v2/user_service.go b/api/v2/user_service.go
index 1e65af5b..72aedc42 100644
--- a/api/v2/user_service.go
+++ b/api/v2/user_service.go
@@ -23,7 +23,7 @@ import (
 )
 
 var (
-	usernameMatcher = regexp.MustCompile("^[a-z]([a-z0-9-]{1,30}[a-z0-9])?$")
+	usernameMatcher = regexp.MustCompile("^[a-z0-9]([a-z0-9-]{1,30}[a-z0-9])$")
 )
 
 type UserService struct {