diff --git a/hostfunc/hostfunc.go b/hostfunc/hostfunc.go
index be3391d2..2b670f00 100644
--- a/hostfunc/hostfunc.go
+++ b/hostfunc/hostfunc.go
@@ -19,6 +19,10 @@ func NewModuleBuilderWith(in map[string]*wasm.Module) *ModuleBuilder {
 	return &ModuleBuilder{modules: in}
 }
 
+func (m *ModuleBuilder) Done() map[string]*wasm.Module {
+	return m.modules
+}
+
 func (m *ModuleBuilder) MustSetFunction(modName, funcName string, fn func(machine *wasm.VirtualMachine) reflect.Value) {
 	if err := m.SetFunction(modName, funcName, fn); err != nil {
 		panic(err)
@@ -34,6 +38,7 @@ func (m *ModuleBuilder) SetFunction(modName, funcName string, fn func(machine *w
 	}
 
 	mod.SecExports[funcName] = &wasm.ExportSegment{
+		Name: funcName,
 		Desc: &wasm.ExportDesc{
 			Kind:  wasm.ExportKindFunction,
 			Index: uint32(len(mod.IndexSpace.Function)),
@@ -81,12 +86,8 @@ func getTypeOf(kind reflect.Kind) (wasm.ValueType, error) {
 	case reflect.Int32, reflect.Uint32:
 		return wasm.ValueTypeI32, nil
 	case reflect.Int64, reflect.Uint64:
-		return wasm.ValueTypeI32, nil
+		return wasm.ValueTypeI64, nil
 	default:
 		return 0x00, fmt.Errorf("invalid type: %s", kind.String())
 	}
 }
-
-func (m *ModuleBuilder) Done() map[string]*wasm.Module {
-	return m.modules
-}
diff --git a/hostfunc/hostfunc_test.go b/hostfunc/hostfunc_test.go
index 86375560..6ec8bc49 100644
--- a/hostfunc/hostfunc_test.go
+++ b/hostfunc/hostfunc_test.go
@@ -1,3 +1,87 @@
 package hostfunc
 
-// fixme:
+import (
+	"reflect"
+	"testing"
+
+	"github.com/mathetake/gasm/wasm"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestModuleBuilder_SetFunction(t *testing.T) {
+	t.Run("register", func(t *testing.T) {
+		builder := NewModuleBuilder()
+		cases := []struct {
+			modName, funcName string
+			expIndex          uint32
+		}{
+			{modName: "env", funcName: "foo", expIndex: 0},
+			{modName: "env", funcName: "bar", expIndex: 1},
+			{modName: "golang", funcName: "hello", expIndex: 0},
+			{modName: "env", funcName: "great", expIndex: 2},
+		}
+
+		for _, c := range cases {
+			builder.MustSetFunction(c.modName, c.funcName, func(machine *wasm.VirtualMachine) reflect.Value {
+				return reflect.ValueOf(func() {})
+			})
+		}
+
+		ms := builder.Done()
+		for _, c := range cases {
+			mod, ok := ms[c.modName]
+			require.True(t, ok)
+			e, ok := mod.SecExports[c.funcName]
+			require.True(t, ok)
+			require.Equal(t, c.funcName, e.Name)
+			require.Equal(t, wasm.ExportKindFunction, e.Desc.Kind)
+			require.Equal(t, c.expIndex, e.Desc.Index)
+		}
+	})
+
+	t.Run("type", func(t *testing.T) {
+		builder := NewModuleBuilder()
+		builder.MustSetFunction("a", "b", func(machine *wasm.VirtualMachine) reflect.Value {
+			return reflect.ValueOf(func(int32, int64) (float32, float64, int32) {
+				return 0, 0, 0
+			})
+		})
+		ms := builder.Done()
+		mod, ok := ms["a"]
+		require.True(t, ok)
+		actualType := mod.IndexSpace.Function[0].FunctionType()
+		require.Equal(t, &wasm.FunctionType{
+			InputTypes:  []wasm.ValueType{wasm.ValueTypeI32, wasm.ValueTypeI64},
+			ReturnTypes: []wasm.ValueType{wasm.ValueTypeF32, wasm.ValueTypeF64, wasm.ValueTypeI32},
+		}, actualType)
+	})
+}
+
+func Test_getSignature(t *testing.T) {
+	v := reflect.ValueOf(func(int32, int64, float32, float64) (int32, float64) { return 0, 0 })
+	actual, err := getSignature(v.Type())
+	require.NoError(t, err)
+	require.Equal(t, &wasm.FunctionType{
+		InputTypes:  []wasm.ValueType{wasm.ValueTypeI32, wasm.ValueTypeI64, wasm.ValueTypeF32, wasm.ValueTypeF64},
+		ReturnTypes: []wasm.ValueType{wasm.ValueTypeI32, wasm.ValueTypeF64},
+	}, actual)
+}
+
+func Test_getTypeOf(t *testing.T) {
+	for _, c := range []struct {
+		kind reflect.Kind
+		exp  wasm.ValueType
+	}{
+		{kind: reflect.Int32, exp: wasm.ValueTypeI32},
+		{kind: reflect.Uint32, exp: wasm.ValueTypeI32},
+		{kind: reflect.Int64, exp: wasm.ValueTypeI64},
+		{kind: reflect.Uint64, exp: wasm.ValueTypeI64},
+		{kind: reflect.Float32, exp: wasm.ValueTypeF32},
+		{kind: reflect.Float64, exp: wasm.ValueTypeF64},
+	} {
+		actual, err := getTypeOf(c.kind)
+		require.NoError(t, err)
+		assert.Equal(t, c.exp, actual)
+	}
+}
diff --git a/wasm/segment.go b/wasm/segment.go
index b0ea4456..b73a77bc 100644
--- a/wasm/segment.go
+++ b/wasm/segment.go
@@ -118,10 +118,10 @@ type ExportDesc struct {
 }
 
 const (
-	ExportKindFunction = 0x00
-	ExportKindTable    = 0x01
-	ExportKindMem      = 0x02
-	ExportKindGlobal   = 0x03
+	ExportKindFunction byte = 0x00
+	ExportKindTable    byte = 0x01
+	ExportKindMem      byte = 0x02
+	ExportKindGlobal   byte = 0x03
 )
 
 func readExportDesc(r io.Reader) (*ExportDesc, error) {