diff --git a/audio/mp3/decode_js.go b/audio/mp3/decode_js.go
index 002117f50..a88f0678c 100644
--- a/audio/mp3/decode_js.go
+++ b/audio/mp3/decode_js.go
@@ -24,8 +24,8 @@ import (
 	"math"
 	"time"
 
-	"github.com/gopherjs/gopherjs/js"
 	"github.com/hajimehoshi/ebiten/audio"
+	"github.com/hajimehoshi/gopherwasm/js"
 )
 
 // TODO: This just uses decodeAudioData, that can treat audio files other than MP3.
@@ -159,7 +159,7 @@ func Decode(context *audio.Context, src audio.ReadSeekCloser) (*Stream, error) {
 	return s, nil
 }
 
-var offlineAudioContextClass *js.Object
+var offlineAudioContextClass = js.Null
 
 func init() {
 	if klass := js.Global.Get("OfflineAudioContext"); klass != js.Undefined {
@@ -173,7 +173,7 @@ func init() {
 }
 
 func decode(context *audio.Context, buf []byte, try int) (*Stream, error) {
-	if offlineAudioContextClass == nil {
+	if offlineAudioContextClass == js.Null {
 		return nil, errors.New("audio/mp3: OfflineAudioContext is not available")
 	}
 
@@ -186,27 +186,30 @@ func decode(context *audio.Context, buf []byte, try int) (*Stream, error) {
 
 	// TODO: 1 is a correct second argument?
 	oc := offlineAudioContextClass.New(2, 1, context.SampleRate())
-	oc.Call("decodeAudioData", js.NewArrayBuffer(buf), func(buf *js.Object) {
-		s.leftData = buf.Call("getChannelData", 0).Interface().([]float32)
+	a := js.ValueOf(buf).Get("buffer")
+	oc.Call("decodeAudioData", a, js.NewCallback(func(args []js.Value) {
+		buf := args[0]
+		s.leftData = float32ArrayToSlice(buf.Call("getChannelData", 0))
 		switch n := buf.Get("numberOfChannels").Int(); n {
 		case 1:
 			s.rightData = s.leftData
 			close(ch)
 		case 2:
-			s.rightData = buf.Call("getChannelData", 1).Interface().([]float32)
+			s.rightData = float32ArrayToSlice(buf.Call("getChannelData", 1))
 			close(ch)
 		default:
 			ch <- fmt.Errorf("audio/mp3: number of channels must be 1 or 2 but %d", n)
 		}
-	}, func(err *js.Object) {
-		if err != nil {
+	}), js.NewCallback(func(args []js.Value) {
+		err := args[0]
+		if err != js.Null || err != js.Undefined {
 			ch <- fmt.Errorf("audio/mp3: decodeAudioData failed: %v", err)
 		} else {
 			// On Safari, error value might be null and it is needed to retry decoding
 			// from the next frame (#438).
 			ch <- errTryAgain
 		}
-	})
+	}))
 
 	timeout := time.Duration(math.Pow(2, float64(try))) * time.Second
 
diff --git a/audio/mp3/float32_notwasm.go b/audio/mp3/float32_notwasm.go
new file mode 100644
index 000000000..e897594d6
--- /dev/null
+++ b/audio/mp3/float32_notwasm.go
@@ -0,0 +1,26 @@
+// Copyright 2018 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build js,!wasm
+
+package mp3
+
+import (
+	gjs "github.com/gopherjs/gopherjs/js"
+	"github.com/hajimehoshi/gopherwasm/js"
+)
+
+func float32ArrayToSlice(arr js.Value) []float32 {
+	return js.GetInternalObject(arr).(*gjs.Object).Interface().([]float32)
+}
diff --git a/audio/mp3/float32_wasm.go b/audio/mp3/float32_wasm.go
new file mode 100644
index 000000000..a11258c25
--- /dev/null
+++ b/audio/mp3/float32_wasm.go
@@ -0,0 +1,37 @@
+// Copyright 2018 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build js,wasm
+
+package mp3
+
+import (
+	"reflect"
+	"syscall/js"
+	"unsafe"
+)
+
+func float32ArrayToSlice(arr js.Value) []float32 {
+	bytes := make([]byte, arr.Length()*4)
+	js.ValueOf(bytes).Call("set", arr.Get("buffer"))
+
+	bh := (*reflect.SliceHeader)(unsafe.Pointer(&bytes))
+	var f []float32
+	fh := (*reflect.SliceHeader)(unsafe.Pointer(&f))
+
+	fh.Data = bh.Data
+	fh.Len = bh.Len / 4
+	fh.Cap = bh.Cap / 4
+	return f
+}