diff --git a/board/main.c b/board/main.c
index 34a5297..82b11b8 100644
--- a/board/main.c
+++ b/board/main.c
@@ -530,10 +530,12 @@ int usb_cb_control_msg(USB_Setup_TypeDef *setup, uint8_t *resp) {
       break;
     case 0xe1: // uart set baud rate
       ur = get_ring_by_number(setup->b.wValue.w);
+      if (!ur) break;
       uart_set_baud(ur->uart, setup->b.wIndex.w);
       break;
     case 0xe2: // uart set parity
       ur = get_ring_by_number(setup->b.wValue.w);
+      if (!ur) break;
       switch (setup->b.wIndex.w) {
         case 0:
           // disable parity
diff --git a/lib/panda.py b/lib/panda.py
index bc40d50..af37f97 100644
--- a/lib/panda.py
+++ b/lib/panda.py
@@ -133,7 +133,7 @@ class Panda(object):
   # ******************* serial *******************
 
   def serial_read(self, port_number):
-    return self.handle.controlRead(usb1.TYPE_VENDOR | usb1.RECIPIENT_DEVICE, 0xe0, port_number, 0, 0x100)
+    return self.handle.controlRead(usb1.TYPE_VENDOR | usb1.RECIPIENT_DEVICE, 0xe0, port_number, 0, 0x40)
 
   def serial_write(self, port_number, ln):
     return self.handle.bulkWrite(2, chr(port_number) + ln)
@@ -148,7 +148,7 @@ class Panda(object):
     # drain buffer
     bret = ""
     while 1:
-      ret = self.handle.controlRead(usb1.TYPE_VENDOR | usb1.RECIPIENT_DEVICE, 0xe0, bus, 0, 0x100)
+      ret = self.handle.controlRead(usb1.TYPE_VENDOR | usb1.RECIPIENT_DEVICE, 0xe0, bus, 0, 0x40)
       if len(ret) == 0:
         break
       bret += str(ret)