diff --git a/src/psi.c b/src/psi.c
index b084a0bc..99d24993 100644
--- a/src/psi.c
+++ b/src/psi.c
@@ -191,7 +191,8 @@ psi_build_pat(th_transport_t *t, uint8_t *buf, int maxlen, int pmtpid)
  * Parser for CA descriptor, viaccess
  */
 static int
-psi_desc_ca_viaccess(th_transport_t *t, th_stream_t *st, uint8_t *ptr, int len)
+psi_desc_ca_viaccess(th_transport_t *t, th_stream_t *st, 
+		     const uint8_t *ptr, int len)
 {
   uint8_t tag, tlen;
   uint32_t id;
@@ -227,7 +228,7 @@ psi_desc_ca_viaccess(th_transport_t *t, th_stream_t *st, uint8_t *ptr, int len)
  * Parser for CA descriptor
  */
 static int
-psi_desc_ca(th_transport_t *t, uint8_t *ptr, int len)
+psi_desc_ca(th_transport_t *t, const uint8_t *ptr, int len)
 {
   uint16_t pid = (ptr[2] & 0x1f) << 8 | ptr[3];
   th_stream_t *st;
@@ -262,7 +263,7 @@ psi_desc_ca(th_transport_t *t, uint8_t *ptr, int len)
  * PMT parser, from ISO 13818-1 and ETSI EN 300 468
  */
 int
-psi_parse_pmt(th_transport_t *t, uint8_t *ptr, int len, int chksvcid,
+psi_parse_pmt(th_transport_t *t, const uint8_t *ptr, int len, int chksvcid,
 	      int delete)
 {
   uint16_t pcr_pid, pid;
diff --git a/src/psi.h b/src/psi.h
index e3ace6d3..9ad64c15 100644
--- a/src/psi.h
+++ b/src/psi.h
@@ -35,7 +35,7 @@ int psi_section_reassemble(psi_section_t *ps, uint8_t *data, int len,
 int psi_parse_pat(th_transport_t *t, uint8_t *ptr, int len,
 		  pid_section_callback_t *pmt_callback);
 
-int psi_parse_pmt(th_transport_t *t, uint8_t *ptr, int len, int chksvcid,
+int psi_parse_pmt(th_transport_t *t, const uint8_t *ptr, int len, int chksvcid,
 		  int delete);
 
 uint32_t psi_crc32(uint8_t *data, size_t datalen);