diff --git a/lib/buffer.h b/lib/buffer.h
index eaf4b88..9d453b1 100644
--- a/lib/buffer.h
+++ b/lib/buffer.h
@@ -63,11 +63,11 @@
 
 /* Buffer prototypes. */
 struct buffer *buffer_new (size_t);
-int buffer_write (struct buffer *, void *, size_t);
+int buffer_write (struct buffer *, const void *, size_t);
 void buffer_free (struct buffer *);
 char *buffer_getstr (struct buffer *);
 int buffer_putc (struct buffer *, u_char);
-int buffer_putstr (struct buffer *, char *);
+int buffer_putstr (struct buffer *, const char *);
 void buffer_reset (struct buffer *);
 int buffer_flush_all (struct buffer *, int);
 int buffer_flush_vty_all (struct buffer *, int, int, int);