diff --git a/fx/encoding.c b/fx/encoding.c
index 1ad2683..38fd47f 100644
--- a/fx/encoding.c
+++ b/fx/encoding.c
@@ -1217,11 +1217,8 @@ static bool wchar_is_control(fx_wchar c)
 		return true;
 	}
 
-	if (c == 0xFEFF) {
-		return true;
-	}
-
-	if (c >= 0xFFF9 && c <= 0xFFFB) {
+	/* treat the reserved range as control characters */
+	if (c >= 0xF0000 && c <= 0xFFFFD) {
 		return true;
 	}