diff -Naur sispmctl-2.7-orig/src/sispm_ctl.c sispmctl-2.7/src/sispm_ctl.c
--- sispmctl-2.7-orig/src/sispm_ctl.c	2008-03-17 11:38:32 +0200
+++ sispmctl-2.7/src/sispm_ctl.c	2009-07-23 15:21:20 +0300
@@ -50,7 +50,7 @@
 {
    int  reqtype=0xa1; //USB_DIR_OUT + USB_TYPE_CLASS + USB_RECIP_INTERFACE /*request type*/,
    int  req=0x01;
-   char buffer[6];
+   unsigned char buffer[6];
 
   if ( usb_control_msg(udev /* handle*/,
 		       reqtype,
@@ -67,8 +67,12 @@
       exit(-5);
   }
 
-  sprintf(serial_id, "%02x:%02x:%02x:%02x:%02x", buffer[0],buffer[1],
-	  buffer[2],buffer[3],buffer[4]);
+  sprintf(serial_id, "%02x:%02x:%02x:%02x:%02x",
+		  (unsigned int)buffer[0],
+		  (unsigned int)buffer[1],
+		  (unsigned int)buffer[2],
+		  (unsigned int)buffer[3],
+		  (unsigned int)buffer[4]);
   return serial_id;
 }