diff --git a/ChangeLog b/ChangeLog
index cf2904ea4..3a996def4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2007-06-16  Mathias Hasselmann  <mathias.hasselmann@gmx.de>
+
+	* glib/gstring.c: Correctly use g_printf_string_upper_bound
+	in g_string_append_vprintf. Fixes #447933.
+
 2007-06-15  Sebastian Wilhelmi  <wilhelmi@google.com>
 
 	* docs/reference/glib/tmpl/threads.sgml: Extended the comments on
diff --git a/glib/gstring.c b/glib/gstring.c
index bf15f5829..ed15223d8 100644
--- a/glib/gstring.c
+++ b/glib/gstring.c
@@ -1278,12 +1278,16 @@ g_string_append_vprintf (GString     *string,
 			 const gchar *fmt,
 			 va_list      args)
 {
+  va_list sneak;
   gsize length;
 
   g_return_if_fail (string != NULL);
   g_return_if_fail (fmt != NULL);
 
-  length = g_printf_string_upper_bound (fmt, args);
+  G_VA_COPY (sneak, args);
+  length = g_printf_string_upper_bound (fmt, sneak);
+  va_end (sneak);
+
   g_string_maybe_expand (string, length);
   length = g_vsnprintf (string->str + string->len, length, fmt, args);
   string->len += length;