diff --git a/src/class.c b/src/class.c
index f94f9a933..6eb70dce6 100644
--- a/src/class.c
+++ b/src/class.c
@@ -487,7 +487,7 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
         if (i < argc) {
           ss = to_str(mrb, *sp++);
           s = mrb_str_ptr(ss);
-          if (strlen(s->ptr) != s->len) {
+          if (strlen(s->ptr) < s->len) {
             mrb_raise(mrb, E_ARGUMENT_ERROR, "String contains NUL");
           }
           *ps = s->ptr;