diff -up ./plugins/sudoers/sudoers.c.sudoerslocale ./plugins/sudoers/sudoers.c
--- ./plugins/sudoers/sudoers.c.sudoerslocale	2016-10-06 18:02:34.926199094 +0200
+++ ./plugins/sudoers/sudoers.c	2016-10-06 18:05:09.660837351 +0200
@@ -146,6 +146,7 @@ sudoers_policy_open(unsigned int version
     sigaction_t sa;
     struct sudo_nss *nss;
     struct sudo_nss *nss_next;
+    char *oldlocale;
     debug_decl(sudoers_policy_open, SUDO_DEBUG_PLUGIN)
 
     sudo_version = version;
@@ -201,7 +202,17 @@ sudoers_policy_open(unsigned int version
     set_perms(PERM_INITIAL);
     set_perms(PERM_ROOT);
 
-    /* Open and parse sudoers, set global defaults */
+    /*
+     *  Open and parse sudoers, set global defaults.
+     *  Uses the C locale unless another is specified in sudoers.
+     */
+#ifdef HAVE_SETLOCALE
+    if (!(oldlocale = setlocale(LC_ALL, def_sudoers_locale))) {
+        warningx(_("unable to set locale to \"%s\", using \"C\""), def_sudoers_locale);
+        setlocale(LC_ALL, "C");
+    }
+#endif
+
     for (nss = snl->first; nss != NULL; nss = nss_next) {
         nss_next = nss->next;
         if (nss->open(nss) == 0 && nss->parse(nss) == 0) {
@@ -250,6 +261,15 @@ sudoers_policy_open(unsigned int version
 
     restore_perms();
 
+    /* Restore user's locale. */
+#ifdef HAVE_SETLOCALE
+    if (oldlocale)
+        setlocale(LC_ALL, oldlocale);
+    else
+        warningx(_("unable to restore user's locale, the C locale remains"));
+#endif
+
+
     debug_return_bool(true);
 }