diff --git a/pages/profile.php b/pages/profile.php
index 3649a72..0e8d19d 100644
--- a/pages/profile.php
+++ b/pages/profile.php
@@ -1,4 +1,17 @@
 <?php
+    function setNamePart(string $part, string $value, string $otherPart, string $otherValue) {
+        $query = $RUNTIME['PDO']->prepare('SELECT 1 FROM UserAccounts WHERE '.$part.' = ? AND '.$otherPart.' = ?');
+        $query->execute(array($value, $otherValue));
+
+        if($query->rowCount() != 0) {
+            $statement = $RUNTIME['PDO']->prepare('UPDATE UserAccounts SET '.$part.' = ? WHERE PrincipalID = ?'); 
+            $statement->execute(array($value, $_SESSION['UUID']));
+            return true;
+        }
+
+        return false;
+    }
+
     $statement = $RUNTIME['PDO']->prepare("CREATE TABLE IF NOT EXISTS `iarstates` (`userID` VARCHAR(36) NOT NULL COLLATE 'utf8_unicode_ci', `filesize` BIGINT(20) NOT NULL DEFAULT '0', `iarfilename` VARCHAR(64) NOT NULL COLLATE 'utf8_unicode_ci', `running` INT(1) NOT NULL DEFAULT '0', PRIMARY KEY (`userID`) USING BTREE) COLLATE='utf8_unicode_ci' ENGINE=InnoDB;");
     $statement->execute();
 
@@ -34,25 +47,31 @@
             if($validator->isValid($_POST)) {
                 if(isset($_POST['formInputFeldVorname'])) {
                     $NewFirstName = trim($_POST['formInputFeldVorname']);
-    
+                    
                     if($NewFirstName != "" && $_SESSION['FIRSTNAME'] != $NewFirstName) {
-                        $statement = $RUNTIME['PDO']->prepare('UPDATE UserAccounts SET FirstName = :FirstName WHERE PrincipalID = :PrincipalID'); 
-                        $statement->execute(['FirstName' => $NewFirstName, 'PrincipalID' => $_SESSION['UUID']]);
-                        $_SESSION['FIRSTNAME'] = $NewFirstName;
-                        $_SESSION['USERNAME'] = $_SESSION['FIRSTNAME']." ".$_SESSION['LASTNAME'];
-                        $_SESSION['DISPLAYNAME'] = strtoupper($_SESSION['USERNAME']);
+                        if(setNamePart('FirstName', $NewFirstName, 'LastName', isset($_POST['formInputFeldNachname']) && trim($_POST['formInputFeldNachname']) > 0 ? $_POST['formInputFeldNachname'] : $_SESSION['LASTNAME'])) {
+                            $_SESSION['FIRSTNAME'] = $NewFirstName;
+                            $_SESSION['USERNAME'] = $_SESSION['FIRSTNAME']." ".$_SESSION['LASTNAME'];
+                            $_SESSION['DISPLAYNAME'] = strtoupper($_SESSION['USERNAME']);
+                        }
+                        else {
+                            $_SESSION['profile_info'] = 'Der gewählte Name ist bereits vergeben.';
+                        }
                     }
                 }
             
                 if(isset($_POST['formInputFeldNachname'])) {
                     $NewLastName = trim($_POST['formInputFeldNachname']);
-    
+                    
                     if($NewLastName != "" && $_SESSION['LASTNAME'] != $NewLastName) {
-                        $statement = $RUNTIME['PDO']->prepare('UPDATE UserAccounts SET LastName = :LastName WHERE PrincipalID = :PrincipalID'); 
-                        $statement->execute(['LastName' => $NewLastName, 'PrincipalID' => $_SESSION['UUID']]);
-                        $_SESSION['LASTNAME'] = $NewLastName;
-                        $_SESSION['USERNAME'] = $_SESSION['FIRSTNAME']." ".$_SESSION['LASTNAME'];
-                        $_SESSION['DISPLAYNAME'] = strtoupper($_SESSION['USERNAME']);
+                        if(setNamePart('LastName', $NewLastName, 'FirstName', isset($_POST['formInputFeldVorname']) && trim($_POST['formInputFeldVorname']) > 0 ? $_POST['formInputFeldVorname'] : $_SESSION['FIRSTNAME'])) {
+                            $_SESSION['LASTNAME'] = $NewLastName;
+                            $_SESSION['USERNAME'] = $_SESSION['FIRSTNAME']." ".$_SESSION['LASTNAME'];
+                            $_SESSION['DISPLAYNAME'] = strtoupper($_SESSION['USERNAME']);
+                        }
+                        else {
+                            $_SESSION['profile_info'] = 'Der gewählte Name ist bereits vergeben.';
+                        }
                     }
                 }