diff --git a/action.yml b/action.yml
index 3ccb167..55fdd6b 100644
--- a/action.yml
+++ b/action.yml
@@ -5,8 +5,6 @@ author: Frost Ming
 inputs:
   python-version:
     description: 'Version range or exact version of a Python version to use, using SemVer''s version range syntax.'
-    default: 3.x
-    required: false
   python-version-file:
     description: 'File containing the Python version to use. Example: .python-version'
   architecture:
diff --git a/dist/setup-pdm.js b/dist/setup-pdm.js
index 3d23781..178f70d 100644
--- a/dist/setup-pdm.js
+++ b/dist/setup-pdm.js
@@ -91003,7 +91003,7 @@ function isCacheAvailable() {
 }
 function resolveVersionInputFromDefaultFile() {
   const couples = [
-    [".python-version", getVersionInputFromPlainFile]
+    ["pyproject.toml", getVersionInputFromTomlFile]
   ];
   for (const [versionFile, _fn] of couples) {
     logWarning(
diff --git a/package.json b/package.json
index 03d4b47..0d2c80d 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "setup-pdm",
-  "version": "2.0.0",
+  "version": "4.0.0",
   "packageManager": "pnpm@8.14.3",
   "description": "The GitHub Action for using pdm as the package manager",
   "repository": {
diff --git a/src/utils.ts b/src/utils.ts
index 20b0ce6..8eb7657 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -7,7 +7,7 @@ import { useCpythonVersion } from 'setup-python/src/find-python'
 import { findPyPyVersion } from 'setup-python/src/find-pypy'
 import {
   getVersionInputFromFile,
-  getVersionInputFromPlainFile,
+  getVersionInputFromTomlFile,
   logWarning,
 } from 'setup-python/src/utils'
 import { getExecOutput } from '@actions/exec'
@@ -80,7 +80,7 @@ export function isCacheAvailable(): boolean {
 
 function resolveVersionInputFromDefaultFile(): string[] {
   const couples: [string, (versionFile: string) => string[]][] = [
-    ['.python-version', getVersionInputFromPlainFile],
+    ['pyproject.toml', getVersionInputFromTomlFile],
   ]
   for (const [versionFile, _fn] of couples) {
     logWarning(