diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index c6734d7..8d68eb6 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -2264,7 +2264,7 @@
 static void ssl_calc_finished_ssl(
                 ssl_context *ssl, unsigned char *buf, int from )
 {
-    char *sender;
+    const char *sender;
     md5_context  md5;
     sha1_context sha1;
 
@@ -2296,17 +2296,17 @@
     SSL_DEBUG_BUF( 4, "finished sha1 state", (unsigned char *)
                    sha1.state, sizeof( sha1.state ) );
 
-    sender = ( from == SSL_IS_CLIENT ) ? (char *) "CLNT"
-                                       : (char *) "SRVR";
+    sender = ( from == SSL_IS_CLIENT ) ? "CLNT"
+                                       : "SRVR";
 
     memset( padbuf, 0x36, 48 );
 
-    md5_update( &md5, (unsigned char *) sender, 4 );
+    md5_update( &md5, (const unsigned char *) sender, 4 );
     md5_update( &md5, session->master, 48 );
     md5_update( &md5, padbuf, 48 );
     md5_finish( &md5, md5sum );
 
-    sha1_update( &sha1, (unsigned char *) sender, 4 );
+    sha1_update( &sha1, (const unsigned char *) sender, 4 );
     sha1_update( &sha1, session->master, 48 );
     sha1_update( &sha1, padbuf, 40 );
     sha1_finish( &sha1, sha1sum );
@@ -2341,7 +2341,7 @@
                 ssl_context *ssl, unsigned char *buf, int from )
 {
     int len = 12;
-    char *sender;
+    const char *sender;
     md5_context  md5;
     sha1_context sha1;
     unsigned char padbuf[36];
@@ -2368,13 +2368,13 @@
                    sha1.state, sizeof( sha1.state ) );
 
     sender = ( from == SSL_IS_CLIENT )
-             ? (char *) "client finished"
-             : (char *) "server finished";
+             ? "client finished"
+             : "server finished";
 
     md5_finish(  &md5, padbuf );
     sha1_finish( &sha1, padbuf + 16 );
 
-    ssl->handshake->tls_prf( session->master, 48, sender,
+    ssl->handshake->tls_prf( session->master, 48, (char *) sender,
                              padbuf, 36, buf, len );
 
     SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
@@ -2391,7 +2391,7 @@
                 ssl_context *ssl, unsigned char *buf, int from )
 {
     int len = 12;
-    char *sender;
+    const char *sender;
     sha2_context sha2;
     unsigned char padbuf[32];
 
@@ -2413,12 +2413,12 @@
                    sha2.state, sizeof( sha2.state ) );
 
     sender = ( from == SSL_IS_CLIENT )
-             ? (char *) "client finished"
-             : (char *) "server finished";
+             ? "client finished"
+             : "server finished";
 
     sha2_finish( &sha2, padbuf );
 
-    ssl->handshake->tls_prf( session->master, 48, sender,
+    ssl->handshake->tls_prf( session->master, 48, (char *) sender,
                              padbuf, 32, buf, len );
 
     SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
@@ -2435,7 +2435,7 @@
                 ssl_context *ssl, unsigned char *buf, int from )
 {
     int len = 12;
-    char *sender;
+    const char *sender;
     sha4_context sha4;
     unsigned char padbuf[48];
 
@@ -2457,12 +2457,12 @@
                    sha4.state, sizeof( sha4.state ) );
 
     sender = ( from == SSL_IS_CLIENT )
-             ? (char *) "client finished"
-             : (char *) "server finished";
+             ? "client finished"
+             : "server finished";
 
     sha4_finish( &sha4, padbuf );
 
-    ssl->handshake->tls_prf( session->master, 48, sender,
+    ssl->handshake->tls_prf( session->master, 48, (char *) sender,
                              padbuf, 48, buf, len );
 
     SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
@@ -3039,7 +3039,7 @@
     if( ssl->hostname == NULL )
         return( POLARSSL_ERR_SSL_MALLOC_FAILED );
 
-    memcpy( ssl->hostname, (unsigned char *) hostname,
+    memcpy( ssl->hostname, (const unsigned char *) hostname,
             ssl->hostname_len );
 
     ssl->hostname[ssl->hostname_len] = '\0';