diff --git a/ext/java/org/msgpack/jruby/Factory.java b/ext/java/org/msgpack/jruby/Factory.java
index <HASH>..<HASH> 100644
--- a/ext/java/org/msgpack/jruby/Factory.java
+++ b/ext/java/org/msgpack/jruby/Factory.java
@@ -54,7 +54,7 @@ public class Factory extends RubyObject {
     return Packer.newPacker(ctx, extensionRegistry(), hasSymbolExtType, args);
   }
 
-  @JRubyMethod(name = "unpacker", optional = 1)
+  @JRubyMethod(name = "unpacker", optional = 2)
   public Unpacker unpacker(ThreadContext ctx, IRubyObject[] args) {
     return Unpacker.newUnpacker(ctx, extensionRegistry(), args);
   }
fix to accept 2 arguments (src and options)