diff --git a/objects/builtin_json.go b/objects/builtin_json.go
index d792212..411c50d 100644
--- a/objects/builtin_json.go
+++ b/objects/builtin_json.go
@@ -12,7 +12,7 @@ func builtinToJSON(args ...Object) (Object, error) {
 		return nil, ErrWrongNumArguments
 	}
 
-	v := objectToInterface(args[0])
+	v := ToInterface(args[0])
 	if vErr, isErr := v.(error); isErr {
 		v = vErr.Error()
 	}
diff --git a/objects/builtin_print.go b/objects/builtin_print.go
index 58f2261..66f5e86 100644
--- a/objects/builtin_print.go
+++ b/objects/builtin_print.go
@@ -41,7 +41,7 @@ func builtinPrintf(args ...Object) (Object, error) {
 
 	formatArgs := make([]interface{}, numArgs-1, numArgs-1)
 	for idx, arg := range args[1:] {
-		formatArgs[idx] = objectToInterface(arg)
+		formatArgs[idx] = ToInterface(arg)
 	}
 
 	fmt.Printf(format.Value, formatArgs...)
@@ -70,7 +70,7 @@ func builtinSprintf(args ...Object) (Object, error) {
 
 	formatArgs := make([]interface{}, numArgs-1, numArgs-1)
 	for idx, arg := range args[1:] {
-		formatArgs[idx] = objectToInterface(arg)
+		formatArgs[idx] = ToInterface(arg)
 	}
 
 	s := fmt.Sprintf(format.Value, formatArgs...)
diff --git a/objects/conversion.go b/objects/conversion.go
index 306fdb1..d7cb3a0 100644
--- a/objects/conversion.go
+++ b/objects/conversion.go
@@ -159,8 +159,8 @@ func ToTime(o Object) (v time.Time, ok bool) {
 	return
 }
 
-// objectToInterface attempts to convert an object o to an interface{} value
-func objectToInterface(o Object) (res interface{}) {
+// ToInterface attempts to convert an object o to an interface{} value
+func ToInterface(o Object) (res interface{}) {
 	switch o := o.(type) {
 	case *Int:
 		res = o.Value
@@ -177,27 +177,29 @@ func objectToInterface(o Object) (res interface{}) {
 	case *Array:
 		res = make([]interface{}, len(o.Value))
 		for i, val := range o.Value {
-			res.([]interface{})[i] = objectToInterface(val)
+			res.([]interface{})[i] = ToInterface(val)
 		}
 	case *ImmutableArray:
 		res = make([]interface{}, len(o.Value))
 		for i, val := range o.Value {
-			res.([]interface{})[i] = objectToInterface(val)
+			res.([]interface{})[i] = ToInterface(val)
 		}
 	case *Map:
 		res = make(map[string]interface{})
 		for key, v := range o.Value {
-			res.(map[string]interface{})[key] = objectToInterface(v)
+			res.(map[string]interface{})[key] = ToInterface(v)
 		}
 	case *ImmutableMap:
 		res = make(map[string]interface{})
 		for key, v := range o.Value {
-			res.(map[string]interface{})[key] = objectToInterface(v)
+			res.(map[string]interface{})[key] = ToInterface(v)
 		}
 	case *Time:
 		res = o.Value
 	case *Error:
 		res = errors.New(o.String())
+	case *Undefined:
+		res = nil
 	case Object:
 		return o
 	}
diff --git a/script/conversion.go b/script/conversion.go
deleted file mode 100644
index c35c141..0000000
--- a/script/conversion.go
+++ /dev/null
@@ -1,33 +0,0 @@
-package script
-
-import (
-	"github.com/d5/tengo/objects"
-)
-
-func objectToInterface(o objects.Object) interface{} {
-	switch val := o.(type) {
-	case *objects.Array:
-		return val.Value
-	case *objects.Map:
-		return val.Value
-	case *objects.Int:
-		return val.Value
-	case *objects.Float:
-		return val.Value
-	case *objects.Bool:
-		if val == objects.TrueValue {
-			return true
-		}
-		return false
-	case *objects.Char:
-		return val.Value
-	case *objects.String:
-		return val.Value
-	case *objects.Bytes:
-		return val.Value
-	case *objects.Undefined:
-		return nil
-	}
-
-	return o
-}
diff --git a/script/variable.go b/script/variable.go
index c5e01bd..e20d3c0 100644
--- a/script/variable.go
+++ b/script/variable.go
@@ -32,7 +32,7 @@ func (v *Variable) Name() string {
 
 // Value returns an empty interface of the variable value.
 func (v *Variable) Value() interface{} {
-	return objectToInterface(*v.value)
+	return objects.ToInterface(*v.value)
 }
 
 // ValueType returns the name of the value type.
@@ -87,7 +87,7 @@ func (v *Variable) Array() []interface{} {
 	case *objects.Array:
 		var arr []interface{}
 		for _, e := range val.Value {
-			arr = append(arr, objectToInterface(e))
+			arr = append(arr, objects.ToInterface(e))
 		}
 		return arr
 	}
@@ -102,7 +102,7 @@ func (v *Variable) Map() map[string]interface{} {
 	case *objects.Map:
 		kv := make(map[string]interface{})
 		for mk, mv := range val.Value {
-			kv[mk] = objectToInterface(mv)
+			kv[mk] = objects.ToInterface(mv)
 		}
 		return kv
 	}