diff --git a/compiler/cpp/src/generate/t_rb_generator.cc b/compiler/cpp/src/generate/t_rb_generator.cc
index 8ae4405..895026f 100644
--- a/compiler/cpp/src/generate/t_rb_generator.cc
+++ b/compiler/cpp/src/generate/t_rb_generator.cc
@@ -620,9 +620,13 @@
   indent_down();
   out << endl;
   indent(out) << "}" << endl << endl;
-  
+
+  // Generate the pre-sorted array of field ids, used for iterating through the fields in sorted order.
+  indent(out) << "FIELD_IDS = FIELDS.keys.sort" << endl << endl;
+
   indent(out) << "def struct_fields; FIELDS; end" << endl << endl;
-  
+
+  indent(out) << "def struct_field_ids; FIELD_IDS; end" << endl << endl;
 }
 
 void t_rb_generator::generate_field_data(std::ofstream& out, t_type* field_type,
diff --git a/lib/rb/ext/constants.h b/lib/rb/ext/constants.h
index 57df544..38b1d61 100644
--- a/lib/rb/ext/constants.h
+++ b/lib/rb/ext/constants.h
@@ -77,6 +77,7 @@
 extern ID native_qmark_method_id;
 
 extern ID fields_const_id;
+extern ID field_ids_const_id;
 extern ID transport_ivar_id;
 extern ID strict_read_ivar_id;
 extern ID strict_write_ivar_id;
diff --git a/lib/rb/ext/struct.c b/lib/rb/ext/struct.c
index 90c4b05..4455c1c 100644
--- a/lib/rb/ext/struct.c
+++ b/lib/rb/ext/struct.c
@@ -58,6 +58,7 @@
 
 #define IS_CONTAINER(ttype) ((ttype) == TTYPE_MAP || (ttype) == TTYPE_LIST || (ttype) == TTYPE_SET)
 #define STRUCT_FIELDS(obj) rb_const_get(CLASS_OF(obj), fields_const_id)
+#define STRUCT_FIELD_IDS(obj) rb_const_get(CLASS_OF(obj), field_ids_const_id)
 
 //-------------------------------------------
 // Writing section
@@ -375,9 +376,7 @@
 
   // iterate through all the fields here
   VALUE struct_fields = STRUCT_FIELDS(self);
-
-  VALUE struct_field_ids_unordered = rb_funcall(struct_fields, keys_method_id, 0);
-  VALUE struct_field_ids_ordered = rb_funcall(struct_field_ids_unordered, sort_method_id, 0);
+  VALUE struct_field_ids_ordered = STRUCT_FIELD_IDS(self);
 
   int i = 0;
   for (i=0; i < RARRAY_LEN(struct_field_ids_ordered); i++) {
diff --git a/lib/rb/ext/thrift_native.c b/lib/rb/ext/thrift_native.c
index 09b9fe4..2a61a3e 100644
--- a/lib/rb/ext/thrift_native.c
+++ b/lib/rb/ext/thrift_native.c
@@ -92,6 +92,7 @@
 
 // constant ids
 ID fields_const_id;
+ID field_ids_const_id;
 ID transport_ivar_id;
 ID strict_read_ivar_id;
 ID strict_write_ivar_id;
@@ -174,6 +175,7 @@
 
   // constant ids
   fields_const_id = rb_intern("FIELDS");
+  field_ids_const_id = rb_intern("FIELD_IDS");
   transport_ivar_id = rb_intern("@trans");
   strict_read_ivar_id = rb_intern("@strict_read");
   strict_write_ivar_id = rb_intern("@strict_write");  
diff --git a/lib/rb/lib/thrift/struct_union.rb b/lib/rb/lib/thrift/struct_union.rb
index 849c856..8627508 100644
--- a/lib/rb/lib/thrift/struct_union.rb
+++ b/lib/rb/lib/thrift/struct_union.rb
@@ -33,7 +33,7 @@
     end
 
     def each_field
-      struct_fields.keys.sort.each do |fid|
+      struct_field_ids.each do |fid|
         data = struct_fields[fid]
         yield fid, data
       end