diff --git a/spec/ruby/optional/capi/ext/exception_spec.c b/spec/ruby/optional/capi/ext/exception_spec.c
index e0d96b55e9..c3b94d7bcd 100644
--- a/spec/ruby/optional/capi/ext/exception_spec.c
+++ b/spec/ruby/optional/capi/ext/exception_spec.c
@@ -36,9 +36,11 @@ VALUE exception_spec_rb_set_errinfo(VALUE self, VALUE exc) {
   return Qnil;
 }
 
+NORETURN(VALUE exception_spec_rb_error_frozen_object(VALUE self, VALUE object));
+
 VALUE exception_spec_rb_error_frozen_object(VALUE self, VALUE object) {
-    rb_error_frozen_object(object);
-    return Qnil;
+  rb_error_frozen_object(object);
+  UNREACHABLE_RETURN(Qnil);
 }
 
 VALUE exception_spec_rb_syserr_new(VALUE self, VALUE num, VALUE msg) {