diff --git a/gluamapper.go b/gluamapper.go
index f23cc66..51b7f25 100644
--- a/gluamapper.go
+++ b/gluamapper.go
@@ -4,10 +4,11 @@ package gluamapper
 import (
 	"errors"
 	"fmt"
-	"github.com/mitchellh/mapstructure"
-	"github.com/yuin/gopher-lua"
 	"regexp"
 	"strings"
+
+	"github.com/mitchellh/mapstructure"
+	"github.com/yuin/gopher-lua"
 )
 
 // Option is a configuration that is used to create a new mapper.
@@ -18,8 +19,12 @@ type Option struct {
 	// Returns error if unused keys exist.
 	ErrorUnused bool
 
-	// A struct tag name for lua table keys . This defaults to "gluamapper"
+	// A struct tag name for lua table keys. This defaults to "gluamapper"
 	TagName string
+
+	// Metadata contains information about decoding a structure that
+	// is tedious or difficult to get otherwise.
+	Metadata *mapstructure.Metadata
 }
 
 // Mapper maps a lua table to a Go struct pointer.
@@ -50,6 +55,7 @@ func (mapper *Mapper) Map(tbl *lua.LTable, st interface{}) error {
 		Result:           st,
 		TagName:          opt.TagName,
 		ErrorUnused:      opt.ErrorUnused,
+		Metadata:         opt.Metadata,
 	}
 	decoder, err := mapstructure.NewDecoder(config)
 	if err != nil {
@@ -63,13 +69,13 @@ func Map(tbl *lua.LTable, st interface{}) error {
 	return NewMapper(Option{}).Map(tbl, st)
 }
 
-
 // Id is an Option.NameFunc that returns given string as-is.
 func Id(s string) string {
 	return s
 }
 
 var camelre = regexp.MustCompile(`_([a-z])`)
+
 // ToUpperCamelCase is an Option.NameFunc that converts strings from snake case to upper camel case.
 func ToUpperCamelCase(s string) string {
 	return strings.ToUpper(string(s[0])) + camelre.ReplaceAllStringFunc(s[1:len(s)], func(s string) string { return strings.ToUpper(s[1:len(s)]) })
diff --git a/gluamapper_test.go b/gluamapper_test.go
index 265f5e5..4ad67e0 100644
--- a/gluamapper_test.go
+++ b/gluamapper_test.go
@@ -1,10 +1,12 @@
 package gluamapper
 
 import (
-	"github.com/yuin/gopher-lua"
 	"path/filepath"
 	"runtime"
 	"testing"
+
+	"github.com/mitchellh/mapstructure"
+	"github.com/yuin/gopher-lua"
 )
 
 func errorIfNotEqual(t *testing.T, v1, v2 interface{}) {
@@ -137,3 +139,40 @@ func TestError(t *testing.T) {
 		t.Error("invalid error message")
 	}
 }
+
+func TestUnused(t *testing.T) {
+	L := lua.NewState()
+	defer L.Close()
+	if err := L.DoString(`
+    person = {
+      name = "Michel",
+      age  = "31", -- weakly input
+      work_place = "San Jose",
+      role = {
+        {
+          name = "Administrator"
+        },
+        {
+          name = "Operator"
+        }
+      },
+      foo = "unused key foo",
+      bar = "unused key bar"
+    }
+	`); err != nil {
+		t.Error(err)
+	}
+	var person testPerson
+
+	var metadata mapstructure.Metadata
+	opts := Option{
+		Metadata: &metadata,
+	}
+	mapper := NewMapper(opts)
+	if err := mapper.Map(L.GetGlobal("person").(*lua.LTable), &person); err != nil {
+		t.Error(err)
+	}
+
+	errorIfNotEqual(t, "Foo", metadata.Unused[0])
+	errorIfNotEqual(t, "Bar", metadata.Unused[1])
+}