diff --git a/models/issue_assignees.go b/models/issue_assignees.go
index b3511f8b59..10bc2dafbe 100644
--- a/models/issue_assignees.go
+++ b/models/issue_assignees.go
@@ -155,31 +155,26 @@ func toggleUserAssignee(e db.Engine, issue *Issue, assigneeID int64) (removed bo
 	}
 
 	// Check if the submitted user is already assigned, if yes delete him otherwise add him
-	var i int
-	for i = 0; i < len(issue.Assignees); i++ {
+	found := false
+	i := 0
+	for ; i < len(issue.Assignees); i++ {
 		if issue.Assignees[i].ID == assigneeID {
+			found = true
 			break
 		}
 	}
 
 	assigneeIn := IssueAssignees{AssigneeID: assigneeID, IssueID: issue.ID}
 
-	toBeDeleted := i < len(issue.Assignees)
-	if toBeDeleted {
-		issue.Assignees = append(issue.Assignees[:i], issue.Assignees[i:]...)
+	if found {
+		issue.Assignees = append(issue.Assignees[:i], issue.Assignees[i+1:]...)
 		_, err = e.Delete(assigneeIn)
-		if err != nil {
-			return toBeDeleted, err
-		}
 	} else {
 		issue.Assignees = append(issue.Assignees, assignee)
 		_, err = e.Insert(assigneeIn)
-		if err != nil {
-			return toBeDeleted, err
-		}
 	}
 
-	return toBeDeleted, nil
+	return found, err
 }
 
 // MakeIDsFromAPIAssigneesToAdd returns an array with all assignee IDs
diff --git a/services/issue/assignee.go b/services/issue/assignee.go
index 4fdf0029c8..7ccefef78e 100644
--- a/services/issue/assignee.go
+++ b/services/issue/assignee.go
@@ -16,9 +16,10 @@ import (
 // DeleteNotPassedAssignee deletes all assignees who aren't passed via the "assignees" array
 func DeleteNotPassedAssignee(issue *models.Issue, doer *user_model.User, assignees []*user_model.User) (err error) {
 	var found bool
+	oriAssignes := make([]*user_model.User, len(issue.Assignees))
+	_ = copy(oriAssignes, issue.Assignees)
 
-	for _, assignee := range issue.Assignees {
-
+	for _, assignee := range oriAssignes {
 		found = false
 		for _, alreadyAssignee := range assignees {
 			if assignee.ID == alreadyAssignee.ID {