diff --git a/adafruit_wiznet5k/adafruit_wiznet5k.py b/adafruit_wiznet5k/adafruit_wiznet5k.py
index fdbc508..2e8ad06 100644
--- a/adafruit_wiznet5k/adafruit_wiznet5k.py
+++ b/adafruit_wiznet5k/adafruit_wiznet5k.py
@@ -802,11 +802,11 @@ def _read_snrx_rd(self, sock):
         return self._pbuff[0] << 8 | self._pbuff[1]
 
     def _write_snrx_rd(self, sock, data):
-        self._write_socket(sock, REG_SNRX_RD, data >> 8)
+        self._write_socket(sock, REG_SNRX_RD, data >> 8 & 0xFF)
         self._write_socket(sock, REG_SNRX_RD + 1, data & 0xFF)
 
     def _write_sntx_wr(self, sock, data):
-        self._write_socket(sock, REG_SNTX_WR, data >> 8)
+        self._write_socket(sock, REG_SNTX_WR, data >> 8 & 0xFF)
         self._write_socket(sock, REG_SNTX_WR + 1, data & 0xFF)
 
     def _read_sntx_wr(self, sock):