diff --git a/js/deno.ts b/js/deno.ts
index 91f7ae1af844e47c2b68c949d9d34ff8285a0d10..62816b8e15f764179d5c97ca3334d7f5f3933176 100644
--- a/js/deno.ts
+++ b/js/deno.ts
@@ -16,7 +16,7 @@ export { symlinkSync, symlink } from "./symlink";
 export { writeFileSync, writeFile } from "./write_file";
 export { ErrorKind, DenoError } from "./errors";
 export { libdeno } from "./libdeno";
-export { arch, platform } from "./platform";
+export { platform } from "./platform";
 export { trace } from "./trace";
 export { truncateSync, truncate } from "./truncate";
 export const args: string[] = [];
diff --git a/js/platform.ts b/js/platform.ts
index 26fc317a10f4eb119f2579ded812cc6356c5bcfb..704ed074314569fa6d8ee84dace60ee4d4ebb68f 100644
--- a/js/platform.ts
+++ b/js/platform.ts
@@ -1,5 +1,3 @@
-// Dummy. Injected in rollup.config.js
-import { DenoArch, DenoPlatform } from "./types";
-
-export const arch: DenoArch = "unknown";
-export const platform: DenoPlatform = "unknown";
+import { Platform } from "./types";
+// 'platform' is  injected by rollup.config.js at compile time.
+export const platform: Platform = {};
diff --git a/js/platform_test.ts b/js/platform_test.ts
index 80a1d932535dca3f59635bf6bfabed267cb73521..65cd2572d150921fbd253d8d0cb8983d64d4bb53 100644
--- a/js/platform_test.ts
+++ b/js/platform_test.ts
@@ -2,8 +2,10 @@
 import { test, assert } from "./test_util.ts";
 import * as deno from "deno";
 
-test(function transformPlatformSuccess() {
-  // Make sure they are transformed
-  assert(deno.arch !== "unknown");
-  assert(deno.platform !== "unknown");
+test(function platformTransform() {
+  // deno.platform is injected by rollup at compile time. Here
+  // we check it has been properly transformed.
+  const { arch, os } = deno.platform;
+  assert(arch === "x64");
+  assert(os === "mac" || os === "win" || os === "linux");
 });
diff --git a/js/types.ts b/js/types.ts
index 7a7bc44d9a08357d4723e83a6694f3b4d8f8e7f7..3ef8f81e595e141467dc2420a09d01938610dee4 100644
--- a/js/types.ts
+++ b/js/types.ts
@@ -152,28 +152,8 @@ declare global {
   }
 }
 
-// Based on Node's arch
-export type DenoArch =
-  | "arm"
-  | "arm64"
-  | "ia32"
-  | "mips"
-  | "mipsel"
-  | "ppc"
-  | "ppc64"
-  | "s390"
-  | "s390x"
-  | "x32"
-  | "x64"
-  | "unknown";
-
-export type DenoPlatform =
-  | "aix"
-  | "darwin"
-  | "freebsd"
-  | "linux"
-  | "openbsd"
-  | "sunos"
-  | "win32"
-  | "android"
-  | "unknown";
+// Do not add unsupported platforms.
+export interface Platform {
+  arch?: "x64";
+  os?: "mac" | "win" | "linux";
+}
diff --git a/rollup.config.js b/rollup.config.js
index 2fdaee08c04763053758f9a34df2a90377dc9bbd..e08604b006655d04bee372deadb573f3fed8d7be 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -80,7 +80,16 @@ function strings({ include, exclude } = {}) {
   };
 }
 
-// Inject deno.arch/deno.platform from Node's process.arch/process.platform
+const archNodeToDeno = {
+  x64: "x64"
+};
+const osNodeToDeno = {
+  win32: "win",
+  darwin: "mac",
+  linux: "linux"
+};
+
+// Inject deno.platform.arch and deno.platform.os
 function platform({ include, exclude } = {}) {
   if (!include) {
     throw new Error("include option must be passed");
@@ -97,11 +106,11 @@ function platform({ include, exclude } = {}) {
     transform(_code, id) {
       if (filter(id)) {
         // Adapted from https://github.com/rollup/rollup-plugin-inject/blob/master/src/index.js
+        const arch = archNodeToDeno[process.arch];
+        const os = osNodeToDeno[process.platform];
         const magicString = new MagicString(`
-import { DenoArch, DenoPlatform } from "./types";
-export const arch: DenoArch = "${process.arch}";
-export const platform: DenoPlatform = "${process.platform}";`);
-        // arch and platform comes from Node
+import { Platform } from "./types";
+export const platform: Platform = { arch: "${arch}", os:"${os}" };`);
         return {
           code: magicString.toString(),
           map: magicString.generateMap()