1 files changed, 2 insertions, 0 deletions
diff --git a/error.c b/error.c
index 2fcacfaa5b..4758961e93 100644
--- a/error.c
+++ b/error.c
@@ -152,6 +152,8 @@ ruby_only_for_internal_use(const char *func)
 static VALUE
 rb_warning_s_warn(VALUE mod, VALUE str)
 {
+    Check_Type(str, T_STRING);
+    rb_must_asciicompat(str);
     rb_write_error_str(str);
     return Qnil;
 }