diff --git a/files/admin.php b/files/admin.php
index 289d95cb91..04ef6a4e82 100644
--- a/files/admin.php
+++ b/files/admin.php
@@ -29,10 +29,14 @@ OC_Util::checkAdminUser();
 
 $htaccessWorking=(getenv('htaccessWorking')=='true');
 
+$upload_max_filesize = OC_Helper::computerFileSize(ini_get('upload_max_filesize'));
+$post_max_size = OC_Helper::computerFileSize(ini_get('post_max_size'));
+$maxUploadFilesize = OC_Helper::humanFileSize(min($upload_max_filesize, $post_max_size));
 if($_POST) {
 	if(isset($_POST['maxUploadSize'])){
-		$maxUploadFilesize=$_POST['maxUploadSize'];
-		OC_Files::setUploadLimit(OC_Helper::computerFileSize($maxUploadFilesize));
+		if(($setMaxSize = OC_Files::setUploadLimit(OC_Helper::computerFileSize($_POST['maxUploadSize']))) !== false) {
+			$maxUploadFilesize = OC_Helper::humanFileSize($setMaxSize);
+		}
 	}
 	if(isset($_POST['maxZipInputSize'])) {
 		$maxZipInputSize=$_POST['maxZipInputSize'];
@@ -42,10 +46,7 @@ if($_POST) {
 		OC_Config::setValue('allowZipDownload', isset($_POST['allowZipDownload']));
 	}
 }
-$upload_max_filesize = OC_Helper::computerFileSize(ini_get('upload_max_filesize'));
-$post_max_size = OC_Helper::computerFileSize(ini_get('post_max_size'));
-$maxUploadFilesize = min($upload_max_filesize, $post_max_size);
-$maxZipInputSize = OC_Helper::humanfilesize(OC_Config::getValue('maxZipInputSize', OC_Helper::computerFileSize('800 MB')));
+$maxZipInputSize = OC_Helper::humanFileSize(OC_Config::getValue('maxZipInputSize', OC_Helper::computerFileSize('800 MB')));
 $allowZipDownload = intval(OC_Config::getValue('allowZipDownload', true));
 
 OC_App::setActiveNavigationEntry( "files_administration" );
diff --git a/lib/files.php b/lib/files.php
index a68c29ad98..473be51fdd 100644
--- a/lib/files.php
+++ b/lib/files.php
@@ -317,17 +317,46 @@ class OC_Files {
 	/**
 	 * set the maximum upload size limit for apache hosts using .htaccess
 	 * @param int size filesisze in bytes
+	 * @return mixed false on failure, size on success
 	 */
 	static function setUploadLimit($size){
 		$size=OC_Helper::humanFileSize($size);
 		$size=substr($size,0,-1);//strip the B
 		$size=str_replace(' ','',$size); //remove the space between the size and the postfix
-		$content = "ErrorDocument 404 /".OC::$WEBROOT."/core/templates/404.php\n";//custom 404 error page
-		$content.= "php_value upload_max_filesize $size\n";//upload limit
-		$content.= "php_value post_max_size $size\n";
-		$content.= "SetEnv htaccessWorking true\n";
-		$content.= "Options -Indexes\n";
-		@file_put_contents(OC::$SERVERROOT.'/.htaccess', $content); //supress errors in case we don't have permissions for it
+
+		//don't allow user to break his config
+		if(intval($size) == 0) {
+			return false;
+		}
+
+		$htaccess = @file_get_contents(OC::$SERVERROOT.'/.htaccess'); //supress errors in case we don't have permissions for
+		if(!$htaccess) {
+			return false;
+		}
+
+		$phpValueKeys = array(
+			'upload_max_filesize',
+			'post_max_size'
+		);
+
+		foreach($phpValueKeys as $key) {
+		    $pattern = '/php_value '.$key.' (\S)*/';
+		    $setting = 'php_value '.$key.' '.$size;
+		    $hasReplaced = 0;
+		    $content = preg_replace($pattern, $setting, $htaccess, 1, $hasReplaced);
+		    if($content !== NULL) {
+				$htaccess = $content;
+			}
+			if($hasReplaced == 0) {
+				$htaccess .= "\n" . $setting;
+			}
+		}
+
+		//supress errors in case we don't have permissions for it
+		if(@file_put_contents(OC::$SERVERROOT.'/.htaccess', $htaccess)) {
+			return OC_Helper::computerFileSize($size);
+		}
+		return false;
 	}
 
 	/**