singleton.patch

--- a/core/src/main/java/org/jruby/ir/runtime/IRRuntimeHelpers.java
+++ b/core/src/main/java/org/jruby/ir/runtime/IRRuntimeHelpers.java
@@ -1153,7 +1153,7 @@ public class IRRuntimeHelpers {
             throw context.runtime.newTypeError("can't define singleton method \"" + method.getName() + "\" for " + obj.getMetaClass().getBaseName());
         }

-        if (obj.isFrozen()) throw context.runtime.newFrozenError("object");
+        if (obj.isFrozen() && (obj.getSingletonClass() != obj.getMetaClass())) throw context.runtime.newFrozenError("object");

         return obj.getSingletonClass();
     }