diff --git a/webapp/components/Group/GroupMember.vue b/webapp/components/Group/GroupMember.vue
index db5635c1f..830318767 100644
--- a/webapp/components/Group/GroupMember.vue
+++ b/webapp/components/Group/GroupMember.vue
@@ -179,12 +179,17 @@ export default {
     },
     async addMemberToGroup() {
       const newRole = 'usual'
+      if (this.groupMembers.find((member) => member.id === this.slugUser[0].id)) {
+        this.$toast.error(
+          this.$t('group.errors.userAlreadyMember', { slug: this.slugUser[0].slug }),
+        )
+        return
+      }
       try {
         await this.$apollo.mutate({
           mutation: changeGroupMemberRoleMutation(),
           variables: { groupId: this.groupId, userId: this.slugUser[0].id, roleInGroup: newRole },
         })
-        // this.$apollo.queries.GroupMembers.refetch()
         this.$emit('loadGroupMembers')
         this.slugUser = []
         this.form.query = ''
diff --git a/webapp/locales/de.json b/webapp/locales/de.json
index 39fd2de9f..31a514470 100644
--- a/webapp/locales/de.json
+++ b/webapp/locales/de.json
@@ -422,6 +422,9 @@
       "groupName": "Einstellungen für „{name}“",
       "title": "Meine Gruppe ändern"
     },
+    "errors": {
+      "userAlreadyMember": "Nutzer @{slug} ist bereits Mitglied"
+    },
     "follow": "Folge",
     "foundation": "Gründung",
     "general": "Allgemein",
diff --git a/webapp/locales/en.json b/webapp/locales/en.json
index 18b579df4..4b63033c1 100644
--- a/webapp/locales/en.json
+++ b/webapp/locales/en.json
@@ -422,6 +422,9 @@
       "groupName": "Settings Of “{name}”",
       "title": "Edit My Group"
     },
+    "errors": {
+      "userAlreadyMember": "User @{slug} is already a member"
+    },
     "follow": "Follow",
     "foundation": "Foundation",
     "general": "General",