diff --git a/src/pcm-player.d.ts b/src/pcm-player.d.ts
index f8bd514..605b0d6 100644
--- a/src/pcm-player.d.ts
+++ b/src/pcm-player.d.ts
@@ -13,11 +13,11 @@ declare module 'pcm-player' {
     'Float32': Float32Array
   }
   interface option {
-    inputCodec: keyof inputCodecs
-    channels: number
-    sampleRate: number
-    flushTime: number
-    fftSize: 32 | 64 | 128 | 256 | 512 | 1024 | 2048 | 4096 | 8192 | 16384 | 32768
+    inputCodec?: keyof inputCodecs
+    channels?: number
+    sampleRate?: number
+    flushTime?: number
+    fftSize?: 32 | 64 | 128 | 256 | 512 | 1024 | 2048 | 4096 | 8192 | 16384 | 32768
     onstatechange?: (node: AudioContext, event: Event, type: AudioContextState) => void
     onended?: (node: AudioBufferSourceNode, event: Event) => void
   }