diff --git a/lib/libc/locale/setlocale.c b/lib/libc/locale/setlocale.c
index daea2bc1751..cba6a531b48 100644
--- a/lib/libc/locale/setlocale.c
+++ b/lib/libc/locale/setlocale.c
@@ -129,7 +129,7 @@ setlocale(category, locale)
 		if (!env || !*env)
 			env = getenv("LANG");
 
-		if (!env || !*env)
+		if (!env || !*env || strchr(env, '/'))
 			env = "C";
 
 		(void) strncpy(new_categories[category], env, ENCODING_LEN);