diff --git a/gtk/gtktextbufferserialize.c b/gtk/gtktextbufferserialize.c
index 27fe43ab59..b6cf9b34e8 100644
--- a/gtk/gtktextbufferserialize.c
+++ b/gtk/gtktextbufferserialize.c
@@ -703,6 +703,14 @@ typedef struct
   gboolean parsed_tags;
 } ParseInfo;
 
+static void
+set_error (GError              **err,
+           GMarkupParseContext  *context,
+           int                   error_domain,
+           int                   error_code,
+           const char           *format,
+           ...) G_GNUC_PRINTF(5, 6);
+
 static void
 set_error (GError              **err,
            GMarkupParseContext  *context,