diff --git a/ietf/rfc4175.h b/ietf/rfc4175.h
index b4bb78d..0b4b743 100644
--- a/ietf/rfc4175.h
+++ b/ietf/rfc4175.h
@@ -67,7 +67,7 @@ static inline void rfc4175_set_extended_sequence_number(uint8_t *buf, uint16_t n
     buf[1] = number & 0xff;
 }
 
-static inline uint16_t rfc4175_get_extended_sequence_number(uint8_t *buf)
+static inline uint16_t rfc4175_get_extended_sequence_number(const uint8_t *buf)
 {
     return (buf[0] << 8) | buf[1];
 }
@@ -78,7 +78,7 @@ static inline void rfc4175_set_line_length(uint8_t *buf, uint16_t length)
     buf[1] = length & 0xff;
 }
 
-static inline uint16_t rfc4175_get_line_length(uint8_t *buf)
+static inline uint16_t rfc4175_get_line_length(const uint8_t *buf)
 {
     return (buf[0] << 8) | buf[1];
 }
@@ -88,7 +88,7 @@ static inline void rfc4175_set_line_field_id(uint8_t *buf, uint8_t id)
     buf[2] |= (!!id) << 7;
 }
 
-static inline uint8_t rfc4175_get_line_field_id(uint8_t *buf)
+static inline uint8_t rfc4175_get_line_field_id(const uint8_t *buf)
 {
     return buf[2] >> 7;
 }
@@ -99,7 +99,7 @@ static inline void rfc4175_set_line_number(uint8_t *buf, uint16_t number)
     buf[3]  = number & 0xff;
 }
 
-static inline uint16_t rfc4175_get_line_number(uint8_t *buf)
+static inline uint16_t rfc4175_get_line_number(const uint8_t *buf)
 {
     return ((buf[2] & 0x7f) << 8) | buf[3];
 }
@@ -109,7 +109,7 @@ static inline void rfc4175_set_line_continuation(uint8_t *buf, uint8_t continuat
     buf[4] |= (!!continuation) << 7;
 }
 
-static inline uint8_t rfc4175_get_line_continuation(uint8_t *buf)
+static inline uint8_t rfc4175_get_line_continuation(const uint8_t *buf)
 {
     return buf[4] >> 7;
 }
@@ -120,7 +120,7 @@ static inline void rfc4175_set_line_offset(uint8_t *buf, uint16_t offset)
     buf[5]  = offset & 0xff;
 }
 
-static inline uint16_t rfc4175_get_line_offset(uint8_t *buf)
+static inline uint16_t rfc4175_get_line_offset(const uint8_t *buf)
 {
     return ((buf[4] & 0x7f) << 8) | buf[5];
 }