diff --git a/src/dns.c b/src/dns.c
index 6eecab2..be6559d 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -50,7 +50,7 @@ int dnsc_use_edns0 = 1;
 #define CHECKLEN(x) if (buflen < (x) + (unsigned)(p-buf))  return 0
 
 int
-dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_t datalen)
+dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, const char *data, size_t datalen)
 {
 	HEADER *header;
 	short name;
@@ -120,7 +120,7 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
 			   For SRV, see RFC2782.
 			 */
 
-			char *mxdata = data;
+			const char *mxdata = data;
 			char *startp;
 			int namelen;
 
diff --git a/src/dns.h b/src/dns.h
index b5d83b2..ce48d1a 100644
--- a/src/dns.h
+++ b/src/dns.h
@@ -27,7 +27,7 @@ typedef enum {
 
 extern int dnsc_use_edns0;
 
-int dns_encode(char *, size_t, struct query *, qr_t, char *, size_t);
+int dns_encode(char *, size_t, struct query *, qr_t, const char *, size_t);
 int dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomain);
 int dns_encode_a_response(char *buf, size_t buflen, struct query *q);
 unsigned short dns_get_id(char *packet, size_t packetlen);
diff --git a/src/encoding.c b/src/encoding.c
index 4906a6b..55b9e2e 100644
--- a/src/encoding.c
+++ b/src/encoding.c
@@ -22,7 +22,7 @@
 int
 build_hostname(char *buf, size_t buflen,
 		const char *data, const size_t datalen,
-		const char *topdomain, struct encoder *encoder, int maxlen)
+		const char *topdomain, const struct encoder *encoder, int maxlen)
 {
 	size_t space;
 	char *b;
@@ -56,7 +56,7 @@ build_hostname(char *buf, size_t buflen,
 }
 
 int
-unpack_data(char *buf, size_t buflen, char *data, size_t datalen, struct encoder *enc)
+unpack_data(char *buf, size_t buflen, char *data, size_t datalen, const struct encoder *enc)
 {
 	if (!enc->eats_dots())
 		datalen = inline_undotify(data, datalen);
diff --git a/src/encoding.h b/src/encoding.h
index abb82da..a75a312 100644
--- a/src/encoding.h
+++ b/src/encoding.h
@@ -26,7 +26,7 @@
 #define DOWNCODECCHECK1_LEN  48
 
 struct encoder {
-	char name[8];
+	const char name[8];
 	int (*encode) (char *, size_t *, const void *, size_t);
 	int (*decode) (void *, size_t *, const char *, size_t);
 	int (*places_dots) (void);
@@ -35,10 +35,9 @@ struct encoder {
 	int (*blocksize_encoded)(void);
 };
 
-int build_hostname(char *, size_t, const char *, const size_t, const char *, struct encoder *, int);
-int unpack_data(char *, size_t, char *, size_t, struct encoder *);
+int build_hostname(char *, size_t, const char *, const size_t, const char *, const struct encoder *, int);
+int unpack_data(char *, size_t, char *, size_t, const struct encoder *);
 int inline_dotify(char *, size_t);
 int inline_undotify(char *, size_t);
 
-
 #endif /* _ENCODING_H_ */
diff --git a/src/iodined.c b/src/iodined.c
index 2fd0611..bd5afdb 100644
--- a/src/iodined.c
+++ b/src/iodined.c
@@ -119,7 +119,7 @@ struct dnsfd {
 };
 
 static int read_dns(int fd, struct dnsfd *dns_fds, int tun_fd, struct query *q);
-static void write_dns(int fd, struct query *q, char *data, int datalen, char downenc);
+static void write_dns(int fd, struct query *q, const char *data, int datalen, char downenc);
 static void handle_full_packet(int tun_fd, struct dnsfd *dns_fds, int userid);
 
 static int
@@ -2118,7 +2118,7 @@ read_dns(int fd, struct dnsfd *dns_fds, int tun_fd, struct query *q)
 }
 
 static size_t
-write_dns_nameenc(char *buf, size_t buflen, char *data, int datalen, char downenc)
+write_dns_nameenc(char *buf, size_t buflen, const char *data, int datalen, char downenc)
 /* Returns #bytes of data that were encoded */
 {
 	static int td1 = 0;
@@ -2188,7 +2188,7 @@ write_dns_nameenc(char *buf, size_t buflen, char *data, int datalen, char downen
 }
 
 static void
-write_dns(int fd, struct query *q, char *data, int datalen, char downenc)
+write_dns(int fd, struct query *q, const char *data, int datalen, char downenc)
 {
 	char buf[64*1024];
 	int len = 0;
diff --git a/src/read.c b/src/read.c
index 51c3bb0..1890359 100644
--- a/src/read.c
+++ b/src/read.c
@@ -230,7 +230,7 @@ putlong(char **dst, uint32_t value)
 }
 
 int
-putdata(char **dst, char *data, size_t len)
+putdata(char **dst, const char *data, size_t len)
 {
 	memcpy(*dst, data, len);
 
@@ -239,7 +239,7 @@ putdata(char **dst, char *data, size_t len)
 }
 
 int
-puttxtbin(char **buf, size_t bufremain, char *from, size_t fromremain)
+puttxtbin(char **buf, size_t bufremain, const char *from, size_t fromremain)
 {
 	unsigned char uc;
 	unsigned char *ucp = &uc;
diff --git a/src/read.h b/src/read.h
index 5da474d..a727c0e 100644
--- a/src/read.h
+++ b/src/read.h
@@ -28,7 +28,7 @@ int putname(char **, size_t, const char *);
 int putbyte(char **, unsigned char);
 int putshort(char **, unsigned short);
 int putlong(char **, uint32_t);
-int putdata(char **, char *, size_t);
-int puttxtbin(char **, size_t, char *, size_t);
+int putdata(char **, const char *, size_t);
+int puttxtbin(char **, size_t, const char *, size_t);
 
 #endif
diff --git a/src/user.c b/src/user.c
index db76e39..b6a48e6 100644
--- a/src/user.c
+++ b/src/user.c
@@ -161,7 +161,7 @@ int find_available_user(void)
 	return ret;
 }
 
-void user_switch_codec(int userid, struct encoder *enc)
+void user_switch_codec(int userid, const struct encoder *enc)
 {
 	if (userid < 0 || userid >= usercount)
 		return;
diff --git a/src/user.h b/src/user.h
index c6aa523..6612bc8 100644
--- a/src/user.h
+++ b/src/user.h
@@ -51,7 +51,7 @@ struct tun_user {
 	struct packet inpacket;
 	struct packet outpacket;
 	int outfragresent;
-	struct encoder *encoder;
+	const struct encoder *encoder;
 	char downenc;
 	int out_acked_seqno;
 	int out_acked_fragment;
@@ -84,7 +84,7 @@ const char* users_get_first_ip(void);
 int find_user_by_ip(uint32_t);
 int all_users_waiting_to_send(void);
 int find_available_user(void);
-void user_switch_codec(int userid, struct encoder *enc);
+void user_switch_codec(int userid, const struct encoder *enc);
 void user_set_conn_type(int userid, enum connection c);
 
 #endif