diff --git a/apps/user_ldap/lib/Group_LDAP.php b/apps/user_ldap/lib/Group_LDAP.php
index b3ff63d3b5c0f..544c7f151ac63 100644
--- a/apps/user_ldap/lib/Group_LDAP.php
+++ b/apps/user_ldap/lib/Group_LDAP.php
@@ -56,9 +56,9 @@
 class Group_LDAP extends ABackend implements GroupInterface, IGroupLDAP, IGetDisplayNameBackend, IDeleteGroupBackend {
 	protected bool $enabled = false;
 
-	/** @var CappedMemoryCache<string[]> $cachedGroupMembers array of users with gid as key */
+	/** @var CappedMemoryCache<string[]> $cachedGroupMembers array of user DN with gid as key */
 	protected CappedMemoryCache $cachedGroupMembers;
-	/** @var CappedMemoryCache<array[]> $cachedGroupsByMember array of groups with uid as key */
+	/** @var CappedMemoryCache<array[]> $cachedGroupsByMember array of groups with user DN as key */
 	protected CappedMemoryCache $cachedGroupsByMember;
 	/** @var CappedMemoryCache<string[]> $cachedNestedGroups array of groups with gid (DN) as key */
 	protected CappedMemoryCache $cachedNestedGroups;
@@ -1357,4 +1357,35 @@ public function getDisplayName(string $gid): string {
 	public function dn2GroupName(string $dn): string|false {
 		return $this->access->dn2groupname($dn);
 	}
+
+	public function addRelationshipToCaches(string $uid, ?string $dnUser, string $gid): void {
+		$dnGroup = $this->access->groupname2dn($gid);
+		$dnUser ??= $this->access->username2dn($uid);
+		if ($dnUser === false || $dnGroup === false) {
+			return;
+		}
+		if (isset($this->cachedGroupMembers[$gid])) {
+			$this->cachedGroupMembers[$gid] = array_merge($this->cachedGroupMembers[$gid], [$dnUser]);
+		}
+		unset($this->cachedGroupsByMember[$dnUser]);
+		unset($this->cachedNestedGroups[$gid]);
+		$cacheKey = 'inGroup' . $uid . ':' . $gid;
+		$this->access->connection->writeToCache($cacheKey, true);
+		$cacheKeyMembers = 'inGroup-members:' . $gid;
+		if (!is_null($data = $this->access->connection->getFromCache($cacheKeyMembers))) {
+			$this->access->connection->writeToCache($cacheKeyMembers, array_merge($data, [$dnUser]));
+		}
+		$cacheKey = '_groupMembers' . $dnGroup;
+		if (!is_null($data = $this->access->connection->getFromCache($cacheKey))) {
+			$this->access->connection->writeToCache($cacheKey, array_merge($data, [$dnUser]));
+		}
+		$cacheKey = 'getUserGroups' . $uid;
+		if (!is_null($data = $this->access->connection->getFromCache($cacheKey))) {
+			$this->access->connection->writeToCache($cacheKey, array_merge($data, [$gid]));
+		}
+		// These cache keys cannot be easily updated:
+		// $cacheKey = 'usersInGroup-' . $gid . '-' . $search . '-' . $limit . '-' . $offset;
+		// $cacheKey = 'usersInGroup-' . $gid . '-' . $search;
+		// $cacheKey = 'countUsersInGroup-' . $gid . '-' . $search;
+	}
 }
diff --git a/apps/user_ldap/lib/Group_Proxy.php b/apps/user_ldap/lib/Group_Proxy.php
index 114902ff9bad7..bb3941565723b 100644
--- a/apps/user_ldap/lib/Group_Proxy.php
+++ b/apps/user_ldap/lib/Group_Proxy.php
@@ -384,4 +384,8 @@ public function getBackendName(): string {
 	public function searchInGroup(string $gid, string $search = '', int $limit = -1, int $offset = 0): array {
 		return $this->handleRequest($gid, 'searchInGroup', [$gid, $search, $limit, $offset]);
 	}
+
+	public function addRelationshipToCaches(string $uid, ?string $dnUser, string $gid): void {
+		$this->handleRequest($gid, 'addRelationshipToCaches', [$uid, $dnUser, $gid]);
+	}
 }
diff --git a/apps/user_ldap/lib/LoginListener.php b/apps/user_ldap/lib/LoginListener.php
index d2aea689efd95..53d4ccc12b9e5 100644
--- a/apps/user_ldap/lib/LoginListener.php
+++ b/apps/user_ldap/lib/LoginListener.php
@@ -93,7 +93,7 @@ private function updateGroups(IUser $userObject): void {
 				continue;
 			}
 			$this->groupMembershipMapper->insert(GroupMembership::fromParams(['groupid' => $groupId,'userid' => $userId]));
-			// TODO: empty cache to avoid crash
+			$this->groupBackend->addRelationshipToCaches($userId, null, $groupId);
 			$this->dispatcher->dispatchTyped(new UserAddedEvent($groupObject, $userObject));
 			$this->logger->info(
 				__CLASS__ . ' – {user} added to {group}',