diff --git a/src/encode.ts b/src/encode.ts
index 06ed3329..7ca99e8c 100644
--- a/src/encode.ts
+++ b/src/encode.ts
@@ -1,5 +1,6 @@
 import { ExtensionCodec, ExtensionCodecType } from "./ExtensionCodec";
 import { Encoder } from "./Encoder";
+import { WritableBuffer } from "./utils/WritableBuffer";
 
 export type EncodeOptions = Readonly<{
   maxDepth: number;
@@ -8,8 +9,8 @@ export type EncodeOptions = Readonly<{
 
 export const DEFAULT_MAX_DEPTH = 100;
 
-export function encode(value: unknown, options: Partial<EncodeOptions> = {}): Array<number> {
-  const output: Array<number> = [];
+export function encode(value: unknown, options: Partial<EncodeOptions> = {}): Uint8Array {
+  const output = new WritableBuffer();
 
   const context = new Encoder(
     options.maxDepth || DEFAULT_MAX_DEPTH,
@@ -17,5 +18,5 @@ export function encode(value: unknown, options: Partial<EncodeOptions> = {}): Ar
   );
   context.encode(output, value, 1);
 
-  return output;
+  return output.toUint8Array();
 }
diff --git a/src/utils/WritableBuffer.ts b/src/utils/WritableBuffer.ts
new file mode 100644
index 00000000..1ce81660
--- /dev/null
+++ b/src/utils/WritableBuffer.ts
@@ -0,0 +1,35 @@
+import { Writable } from "../Writable";
+
+// Experimental `push(...bytes)`-able buffer
+// Unfortunately, it is always slower than Array<number>.
+
+export class WritableBuffer implements Writable<number> {
+  private length = 0;
+  private buffer = new Uint8Array(128);
+
+  push(...bytes: ReadonlyArray<number>): void {
+    const offset = this.length;
+    const bytesLen = bytes.length;
+    const newLength = offset + bytesLen;
+
+    if (this.buffer.length < newLength) {
+      this.grow(newLength);
+    }
+
+    const buffer = this.buffer;
+    for (let i = 0; i < bytesLen; i++) {
+      buffer[offset + i] = bytes[i];
+    }
+    this.length = newLength;
+  }
+
+  grow(newLength: number) {
+    const newBuffer = new Uint8Array(newLength * 2);
+    newBuffer.set(this.buffer);
+    this.buffer = newBuffer;
+  }
+
+  toUint8Array(): Uint8Array {
+    return this.buffer.subarray(0, this.length);
+  }
+}
diff --git a/tsconfig.json b/tsconfig.json
index 7a09086c..fb5d4ef1 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
     /* Basic Options */
-    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
+    "target": "es2019",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
     "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
     "lib": ["es2019", "dom"],                             /* Specify library files to be included in the compilation. */
     // "allowJs": true,                       /* Allow javascript files to be compiled. */
diff --git a/tsconfig.production.json b/tsconfig.production.json
index d78a9246..a5b54a3b 100644
--- a/tsconfig.production.json
+++ b/tsconfig.production.json
@@ -1,6 +1,7 @@
 {
   "extends": "./tsconfig.json",
   "compilerOptions": {
+    "target": "es5",
     "outDir": "./dist",
     "declaration": true,
     "noEmitOnError": true,