diff --git a/README.md b/README.md
index bb939f2..575f991 100644
--- a/README.md
+++ b/README.md
@@ -30,24 +30,17 @@ Hello, world!
 
 ## How It Works
 
-We can write a program like this:
+When `ctts script.ts` is executed, compile-time-typescript creates a caller like this:
 
 ```typescript
-type Main<Input extends string> = `Hello, ${Input}\n`;
-export default Main;
-```
-
-Compile-time-typescript saves the program as `callee.ts` and creates `caller.ts`:
-
-```typescript
-import Main from './callee';
+import Main from '/path/to/script';
 type Input = "HERE COMES THE INPUT";
 type Output = Main<Input>;
 ```
 
 So the program must have a default export of a generic type that takes a type parameter and constructs a string literal type.
 
-Then compile-time-typescript type-checks `caller.ts` and extracts the type information of `Output`.
+Then compile-time-typescript type-checks the caller and extracts the type information of `Output`.
 
 If `Output` is a string literal type, its content is printed. Otherwise, an error occurs.
 
diff --git a/src/index.ts b/src/index.ts
index fbd00d4..9ff3956 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,6 +3,8 @@ import { promises as fs } from 'fs';
 import * as tmp from 'tmp-promise';
 import * as path from 'path';
 
+tmp.setGracefulCleanup();
+
 interface RunOptions {
   input: Buffer;
 }
@@ -12,24 +14,19 @@ interface RunResult {
 }
 
 export async function run(fileName: string, { input = Buffer.of() }: Partial<RunOptions> = {}): Promise<RunResult> {
-  const { path: tmpDirPath } = await tmp.dir({ prefix: `compile-time-typescript` });
-  const calleeFileName = `callee.ts`;
-  const callerFileName = `caller.ts`;
-  await Promise.all([
-    fs.copyFile(fileName, path.join(tmpDirPath, calleeFileName)),
-    fs.writeFile(path.join(tmpDirPath, callerFileName), `
-      import Main from './${path.basename(calleeFileName, path.extname(calleeFileName))}';
-      type Input = ${JSON.stringify(input.toString('binary'))};
-      type Output = Main<Input>;
-    `),
-  ]);
+  const { path: callerFileName, cleanup } = await tmp.file({ prefix: `compile-time-typescript`, postfix: `caller.ts` });
+  await fs.writeFile(callerFileName, `
+    import Main from ${JSON.stringify(path.resolve(fileName).replace(/\.ts$/, ''))};
+    type Input = ${JSON.stringify(input.toString('binary'))};
+    type Output = Main<Input>;
+  `);
   const program = ts.createProgram({
-    rootNames: [path.join(tmpDirPath, callerFileName)],
+    rootNames: [callerFileName],
     options: {
       strict: true,
     },
   });
-  const source = program.getSourceFile(path.join(tmpDirPath, callerFileName))!;
+  const source = program.getSourceFile(callerFileName)!;
   const checker = program.getTypeChecker();
   const outputList: Buffer[] = [];
 
@@ -47,11 +44,7 @@ export async function run(fileName: string, { input = Buffer.of() }: Partial<Run
   }
 
   source.forEachChild(visit);
-  await Promise.all([
-    fs.unlink(path.join(tmpDirPath, calleeFileName)),
-    fs.unlink(path.join(tmpDirPath, callerFileName)),
-  ]);
-  await fs.rmdir(tmpDirPath);
+  await cleanup();
   return {
     output: Buffer.concat(outputList),
   };