diff --git a/backend/src/apis/humhub/syncUser.ts b/backend/src/apis/humhub/syncUser.ts
index c29d6e29f..f6bdcbbb6 100644
--- a/backend/src/apis/humhub/syncUser.ts
+++ b/backend/src/apis/humhub/syncUser.ts
@@ -49,7 +49,11 @@ export async function syncUser(
   if (!isValid(postUser, user.id)) {
     return ExecutedHumhubAction.VALIDATION_ERROR
   }
-  const humhubUser = humhubUsers.get(postUser.account.username)
+  let humhubUser = humhubUsers.get(postUser.account.username)
+  if (!humhubUser) {
+    // fallback for legacy users
+    humhubUser = humhubUsers.get(user.gradidoID)
+  }
   const humHubClient = HumHubClient.getInstance()
   if (!humHubClient) {
     throw new LogError('Error creating humhub client')
diff --git a/backend/src/graphql/resolver/util/syncHumhub.ts b/backend/src/graphql/resolver/util/syncHumhub.ts
index 5b851fa2f..2716069ac 100644
--- a/backend/src/graphql/resolver/util/syncHumhub.ts
+++ b/backend/src/graphql/resolver/util/syncHumhub.ts
@@ -4,7 +4,9 @@ import { HumHubClient } from '@/apis/humhub/HumHubClient'
 import { GetUser } from '@/apis/humhub/model/GetUser'
 import { PostUser } from '@/apis/humhub/model/PostUser'
 import { ExecutedHumhubAction, syncUser } from '@/apis/humhub/syncUser'
+import { PublishNameLogic } from '@/data/PublishName.logic'
 import { UpdateUserInfosArgs } from '@/graphql/arg/UpdateUserInfosArgs'
+import { PublishNameType } from '@/graphql/enum/PublishNameType'
 import { backendLogger as logger } from '@/server/logger'
 
 /**
@@ -44,7 +46,9 @@ export async function syncHumhub(
   }
   const humhubUsers = new Map<string, GetUser>()
   if (humhubUser) {
-    humhubUsers.set(humhubUser.account.username, humhubUser)
+    const publishNameLogic = new PublishNameLogic(user)
+    const username = publishNameLogic.getUserIdentifier(user.humhubPublishName as PublishNameType)
+    humhubUsers.set(username, humhubUser)
   }
   logger.debug('update user at humhub')
   const result = await syncUser(user, humhubUsers)
diff --git a/frontend/src/locales/de.json b/frontend/src/locales/de.json
index 104d2f61d..0921d5960 100644
--- a/frontend/src/locales/de.json
+++ b/frontend/src/locales/de.json
@@ -418,7 +418,7 @@
       "first": "Vorname",
       "first-tooltip": "Nur der Vornamen",
       "first-initial": "Vorname und Initial",
-      "first-initial-tooltip": "Vornamen plus die ersten beiden Anfangsbuchstabe des Nachnamens",
+      "first-initial-tooltip": "Vornamen plus den ersten Anfangsbuchstaben des Nachnamens",
       "initials": "Initialen",
       "initials-tooltip": "Initialen von Vor- und Nachname also jeweils die ersten zwei Buchstaben unabhängig von der Existenz des Benutzernamens",
       "name-full": "Vorname und Nachname",
diff --git a/frontend/src/locales/en.json b/frontend/src/locales/en.json
index afc5fce89..58c003268 100644
--- a/frontend/src/locales/en.json
+++ b/frontend/src/locales/en.json
@@ -418,7 +418,7 @@
       "first": "Firstname",
       "first-tooltip": "the first name only",
       "first-initial": "First name and initial",
-      "first-initial-tooltip": "first name plus the first two initial letters of the last name",
+      "first-initial-tooltip": "first name plus the first letter of the last name",
       "initials": "Initials",
       "initials-tooltip": "Initials of first name and last name, i.e. the first two letters of each regardless of the existence of the user name",
       "name-full": "first name and last name",