diff --git a/lib/rb/spec/ThriftSpec.thrift b/lib/rb/spec/ThriftSpec.thrift
index 022c786..e04662b 100644
--- a/lib/rb/spec/ThriftSpec.thrift
+++ b/lib/rb/spec/ThriftSpec.thrift
@@ -10,7 +10,8 @@
   3: Hello hello = {'greeting' : "hello, world!"},
   4: list<i32> ints = [1, 2, 2, 3],
   5: map<i32, map<string, double>> complex,
-  6: set<i16> shorts = [5, 17, 239]
+  6: set<i16> shorts = [5, 17, 239],
+  7: optional string opt_string
 }
 
 struct BoolStruct {