diff --git a/src/Client.php b/src/Client.php
index d58e140..1bbe217 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -297,15 +297,25 @@ public function listFiles(array $options)
 
         // B2 returns, at most, 1000 files per "page". Loop through the pages and compile an array of File objects.
         while (true) {
+        	$json = [
+		        'bucketId' => $options['BucketId'],
+		        'startFileName' => $nextFileName,
+		        'maxFileCount' => $maxFileCount,
+	        ];
+
+        	if (isset($options['prefix'])) {
+        		$json['prefix'] = $options['prefix'];
+	        }
+
+	        if (isset($options['delimiter'])) {
+	        	$json['delimiter'] = $options['delimiter'];
+	        }
+
             $response = $this->client->request('POST', $this->apiUrl.'/b2_list_file_names', [
                 'headers' => [
                     'Authorization' => $this->authToken
                 ],
-                'json' => [
-                    'bucketId' => $options['BucketId'],
-                    'startFileName' => $nextFileName,
-                    'maxFileCount' => $maxFileCount,
-                ]
+                'json' => $json
             ]);
 
             foreach ($response['files'] as $file) {