diff --git a/gcc/intl.h b/gcc/intl.h
index 829364ae905..0d91e3f509e 100644
--- a/gcc/intl.h
+++ b/gcc/intl.h
@@ -47,14 +47,18 @@ extern const char *fake_ngettext (const char *singular, const char *plural,
 
 #endif
 
+/* Used to immediately translate the argument.  */
 #ifndef _
 # define _(msgid) gettext (msgid)
 #endif
 
+/* Used to mark strings that will be translated later.  */
 #ifndef N_
 # define N_(msgid) msgid
 #endif
 
+/* Like N_, but for GCC diagnostic format strings.  See ABOUT-GCC-NLS for
+   details.  */
 #ifndef G_
 # define G_(gmsgid) gmsgid
 #endif