diff --git a/drivers/isdn/gigaset/usb-gigaset.c b/drivers/isdn/gigaset/usb-gigaset.c
index 76dbb20..f65cf7d 100644
--- a/drivers/isdn/gigaset/usb-gigaset.c
+++ b/drivers/isdn/gigaset/usb-gigaset.c
@@ -39,7 +39,8 @@
 #define GIGASET_MODULENAME "usb_gigaset"
 #define GIGASET_DEVNAME    "ttyGU"
 
-#define IF_WRITEBUF 2000	/* arbitrary limit */
+/* length limit according to Siemens 3070usb-protokoll.doc ch. 2.1 */
+#define IF_WRITEBUF 264
 
 /* Values for the Gigaset M105 Data */
 #define USB_M105_VENDOR_ID	0x0681