diff --git a/src/intl/gettext/libintl.c b/src/intl/gettext/libintl.c
index cf050cc07..9aa373b46 100644
--- a/src/intl/gettext/libintl.c
+++ b/src/intl/gettext/libintl.c
@@ -133,7 +133,7 @@ iso639_to_language(char *iso639)
 
 int system_language = 0;
 
-char *
+const char *
 language_to_iso639(int language)
 {
 	/* Language is "system", we need to extract the index from
diff --git a/src/intl/gettext/libintl.h b/src/intl/gettext/libintl.h
index 39d44d5fc..311441752 100644
--- a/src/intl/gettext/libintl.h
+++ b/src/intl/gettext/libintl.h
@@ -189,7 +189,7 @@ extern int name_to_language(const char *name);
 extern int iso639_to_language(char *iso639);
 
 extern char *language_to_name(int language);
-extern char *language_to_iso639(int language);
+extern const char *language_to_iso639(int language);
 
 extern int get_system_language_index(void);