diff --git a/modules/rtp.io/rtp_io.c b/modules/rtp.io/rtp_io.c
index 7ef99a3f630..e64c542b003 100644
--- a/modules/rtp.io/rtp_io.c
+++ b/modules/rtp.io/rtp_io.c
@@ -151,13 +151,13 @@ static int mod_init(void)
 
 
         int argc;
-        char **argv = rtp_io_env_gen_argv(&rpi_descp->env, &argc);
+        const char *const *argv = rtp_io_env_gen_argv(&rpi_descp->env, &argc);
         if (argv == NULL)
             goto e1;
 
         OPT_RESTORE();
         rpi_descp->rtpp_cfsp = rtpp_main(argc, argv);
-        free(argv);
+        free((void *)argv);
         if (rpi_descp->rtpp_cfsp == NULL)
             goto e1;
 
diff --git a/modules/rtp.io/rtp_io_util.c b/modules/rtp.io/rtp_io_util.c
index eb987e20ca8..a20626ffed0 100644
--- a/modules/rtp.io/rtp_io_util.c
+++ b/modules/rtp.io/rtp_io_util.c
@@ -42,7 +42,7 @@ rtp_io_env_append(struct rtpp_env_hd *ecp, struct rtpp_env *ep)
         ecp->len += 1;
 }
 
-char **
+const char *const *
 rtp_io_env_gen_argv(struct rtpp_env_hd *ecp, int *lenp)
 {
         char **rval;
@@ -59,5 +59,5 @@ rtp_io_env_gen_argv(struct rtpp_env_hd *ecp, int *lenp)
             ep = ep->next;
         }
         *lenp = ecp->len;
-        return rval;
+        return (const char *const *)rval;
 }
diff --git a/modules/rtp.io/rtp_io_util.h b/modules/rtp.io/rtp_io_util.h
index 23d23b20735..cc4a2ae3a70 100644
--- a/modules/rtp.io/rtp_io_util.h
+++ b/modules/rtp.io/rtp_io_util.h
@@ -1,8 +1,10 @@
+#pragma once
+
 struct rtpp_env;
 struct rtpp_env_hd;
 
 struct rtpp_env *rtp_io_env_asprintf(const char *, ...);
 
 void rtp_io_env_append(struct rtpp_env_hd *, struct rtpp_env *);
-char ** rtp_io_env_gen_argv(struct rtpp_env_hd *, int *);
+const char *const * rtp_io_env_gen_argv(struct rtpp_env_hd *, int *);