Index: t3lib/extjs/class.t3lib_extjs_extdirectapi.php
===================================================================
--- t3lib/extjs/class.t3lib_extjs_extdirectapi.php	(revision 10487)
+++ t3lib/extjs/class.t3lib_extjs_extdirectapi.php	(revision )
@@ -153,7 +153,10 @@
 		if (TYPO3_MODE === 'FE') {
 			$url = t3lib_div::locationHeaderUrl('?eID=ExtDirect&action=route&namespace=');
 		} else {
-			$url = t3lib_div::locationHeaderUrl('ajax.php?ajaxID=ExtDirect::route&namespace=');
+			$url = t3lib_div::locationHeaderUrl(
+				t3lib_div::getIndpEnv('TYPO3_SITE_URL') .
+				'typo3/ajax.php?ajaxID=ExtDirect::route&namespace='
+			);
 		}
 		$url .= rawurlencode($namespace);