diff --git a/include/polarssl/pem.h b/include/polarssl/pem.h
index e95dc10..801c57b 100644
--- a/include/polarssl/pem.h
+++ b/include/polarssl/pem.h
@@ -86,7 +86,7 @@
  *
  * \return          0 on success, ior a specific PEM error code
  */
-int pem_read_buffer( pem_context *ctx, char *header, char *footer,
+int pem_read_buffer( pem_context *ctx, const char *header, const char *footer,
                      const unsigned char *data,
                      const unsigned char *pwd,
                      size_t pwdlen, size_t *use_len );