diff --git a/scripts/build_npm.ts b/scripts/build_npm.ts
index 1ae0b02..f1abbb0 100644
--- a/scripts/build_npm.ts
+++ b/scripts/build_npm.ts
@@ -25,6 +25,7 @@ await build({
 	packageManager: "pnpm",
 	compilerOptions: {
 		lib: ["DOM", "ESNext"],
+		sourceMap: false,
 	},
 	typeCheck: "both",
 	package: {
@@ -51,8 +52,11 @@ await build({
 		},
 		sideEffects: false,
 	},
-	postBuild() {
-		Deno.copyFileSync("LICENSE", "npm/LICENSE");
-		Deno.copyFileSync("README.md", "npm/README.md");
+	async postBuild() {
+		await Deno.copyFile("LICENSE", "npm/LICENSE");
+		await Deno.copyFile("README.md", "npm/README.md");
+		using npmIgnoreFile = await Deno.open("npm/.npmignore", { append: true });
+		const data = new TextEncoder().encode("deps/" + "\n" + "*.map" + "\n");
+		npmIgnoreFile.write(data);
 	},
 });