diff --git a/lib/rtplib.c b/lib/rtplib.c
index 083c8331f..740ab6a54 100644
--- a/lib/rtplib.c
+++ b/lib/rtplib.c
@@ -106,7 +106,7 @@ error:
 }
 
 
-int rtp_padding(struct rtp_header *header, str *payload) {
+int rtp_padding(const struct rtp_header *header, str *payload) {
 	if (!(header->v_p_x_cc & 0x20))
 		return 0; // no padding
 	if (payload->len == 0)
diff --git a/lib/rtplib.h b/lib/rtplib.h
index 86b000553..e2ae14d01 100644
--- a/lib/rtplib.h
+++ b/lib/rtplib.h
@@ -44,7 +44,7 @@ extern const int num_rfc_rtp_payload_types;
 
 
 int rtp_payload(struct rtp_header **out, str *p, const str *s);
-int rtp_padding(struct rtp_header *header, str *payload);
+int rtp_padding(const struct rtp_header *header, str *payload);
 const struct rtp_payload_type *rtp_get_rfc_payload_type(unsigned int type);
 const struct rtp_payload_type *rtp_get_rfc_codec(const str *codec);