diff --git a/crypto/crc16.c b/crypto/crc16.c
index d22b656..0b08e9c 100644
--- a/crypto/crc16.c
+++ b/crypto/crc16.c
@@ -90,7 +90,7 @@
 };
 
 uint16_t
-cyg_crc16(unsigned char *buf, int len)
+cyg_crc16(const unsigned char *buf, int len)
 {
     int i;
     uint16_t cksum;
diff --git a/include/crc.h b/include/crc.h
index 10560c9..4290f41 100644
--- a/include/crc.h
+++ b/include/crc.h
@@ -95,6 +95,6 @@
 
 /* 16 bit CRC with polynomial x^16+x^12+x^5+1 */
 
-extern uint16_t cyg_crc16(unsigned char *s, int len);
+extern uint16_t cyg_crc16(const unsigned char *s, int len);
 
 #endif /* _SERVICES_CRC_CRC_H_ */