diff --git a/programs/ssl/ssl_mail_client.c b/programs/ssl/ssl_mail_client.c
index 8858b1d..72cc289 100644
--- a/programs/ssl/ssl_mail_client.c
+++ b/programs/ssl/ssl_mail_client.c
@@ -612,7 +612,7 @@
         fflush( stdout );
 
         n = sizeof( buf );
-        len = base64_encode( base, &n, opt.user_name, strlen( opt.user_name ) );
+        len = base64_encode( base, &n, (unsigned char *) opt.user_name, strlen( opt.user_name ) );
         len = sprintf( (char *) buf, "%s\n", base );
         ret = write_ssl_and_get_response( &ssl, buf, len );
         if( ret < 300 || ret > 399 )
@@ -626,7 +626,7 @@
         printf( "  > Write password to server: %s", opt.user_pwd );
         fflush( stdout );
 
-        len = base64_encode( base, &n, opt.user_pwd, strlen( opt.user_pwd ) );
+        len = base64_encode( base, &n, (unsigned char *) opt.user_pwd, strlen( opt.user_pwd ) );
         len = sprintf( (char *) buf, "%s\n", base );
         ret = write_ssl_and_get_response( &ssl, buf, len );
         if( ret < 200 || ret > 399 )