diff --git a/src/main/scala/gitbucket/core/service/IssuesService.scala b/src/main/scala/gitbucket/core/service/IssuesService.scala
index ecbfa55..e604e0b 100644
--- a/src/main/scala/gitbucket/core/service/IssuesService.scala
+++ b/src/main/scala/gitbucket/core/service/IssuesService.scala
@@ -435,7 +435,7 @@
 
   def getAssignableUserNames(owner: String, repository: String)(implicit s: Session): List[String] = {
     (getCollaboratorUserNames(owner, repository, Seq(Permission.ADMIN, Permission.WRITE)) :::
-      (if (getAccountByUserName(owner).get.isGroupAccount) getGroupMembers(owner).map(_.userName) else List(owner))).sorted
+      (if (getAccountByUserName(owner).get.isGroupAccount) getGroupMembers(owner).map(_.userName) else List(owner))).distinct.sorted
   }
 
 }