1 files changed, 3 insertions, 0 deletions
diff --git a/class.c b/class.c
index 8addef7612..b7f05dd4e5 100644
--- a/class.c
+++ b/class.c
@@ -92,6 +92,9 @@ rb_class_init_copy(clone, orig)
     if (RCLASS(clone)->super != 0) {
 	rb_raise(rb_eTypeError, "already initialized class");
     }
+    if (FL_TEST(orig, FL_SINGLETON)) {
+	rb_raise(rb_eTypeError, "can't copy singleton class");
+    }
     return rb_mod_init_copy(clone, orig);
 }