diff --git a/libtelnet.h b/libtelnet.h
index a129438..a8bf4da 100644
--- a/libtelnet.h
+++ b/libtelnet.h
@@ -137,7 +137,7 @@
 /* event information */
 struct libtelnet_event_t {
 	/* data buffer: for DATA, SEND, SUBNEGOTIATION, and ERROR events */
-	unsigned char *buffer;
+	const unsigned char *buffer;
 	unsigned int size;
 	/* type of event */ 
 	enum libtelnet_event_type_t type;
@@ -195,7 +195,7 @@
 extern void libtelnet_free(libtelnet_t *telnet);
 
 /* push a byte buffer into the state tracker */
-extern void libtelnet_push(libtelnet_t *telnet, unsigned char *buffer,
+extern void libtelnet_push(libtelnet_t *telnet, const unsigned char *buffer,
 		unsigned int size);
 
 /* send an iac command */
@@ -213,8 +213,8 @@
 		unsigned char opt);
 
 /* send non-command data (escapes IAC bytes) */
-extern void libtelnet_send_data(libtelnet_t *telnet, unsigned char *buffer,
-		unsigned int size);
+extern void libtelnet_send_data(libtelnet_t *telnet,
+		const unsigned char *buffer, unsigned int size);
 
 /* send sub-request, equivalent to:
  *   libtelnet_send_telopt(telnet, LIBTELNET_SB, telopt)
@@ -224,7 +224,7 @@
  * thare are most easily implemented with a series of send_data calls.
  */
 extern void libtelnet_send_subnegotiation(libtelnet_t *telnet,
-		unsigned char telopt, unsigned char *buffer, unsigned int size);
+		unsigned char telopt, const unsigned char *buffer, unsigned int size);
 
 /* begin sending compressed data (server only) */
 extern void libtelnet_begin_compress2(libtelnet_t *telnet);