diff --git a/guile/src/core.c b/guile/src/core.c
index 605c91f7a..38d573fa9 100644
--- a/guile/src/core.c
+++ b/guile/src/core.c
@@ -1,5 +1,5 @@
 /* GnuTLS --- Guile bindings for GnuTLS.
-   Copyright (C) 2007-2014, 2016 Free Software Foundation, Inc.
+   Copyright (C) 2007-2014, 2016-2017 Free Software Foundation, Inc.
 
    GnuTLS is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
@@ -1428,22 +1428,19 @@ set_certificate_file (certificate_set_file_function_t set_file,
 {
   int err;
   char *c_file;
-  size_t c_file_len;
 
   gnutls_certificate_credentials_t c_cred;
   gnutls_x509_crt_fmt_t c_format;
 
   c_cred = scm_to_gnutls_certificate_credentials (cred, 1, FUNC_NAME);
   SCM_VALIDATE_STRING (2, file);
-  c_format = scm_to_gnutls_x509_certificate_format (format, 3, FUNC_NAME);
-
-  c_file_len = scm_c_string_length (file);
-  c_file = alloca (c_file_len + 1);
 
-  (void) scm_to_locale_stringbuf (file, c_file, c_file_len + 1);
-  c_file[c_file_len] = '\0';
+  c_format = scm_to_gnutls_x509_certificate_format (format, 3, FUNC_NAME);
+  c_file = scm_to_locale_string (file);
 
   err = set_file (c_cred, c_file, c_format);
+  free (c_file);
+
   if (EXPECT_FALSE (err < 0))
     scm_gnutls_error (err, FUNC_NAME);