diff --git a/common.js b/common.js
index d16152c..de7293c 100644
--- a/common.js
+++ b/common.js
@@ -40,6 +40,25 @@ export function isStableVersion(rubyVersion) {
   return /^\d+(\.\d+)*$/.test(rubyVersion)
 }
 
+export function isBundler2Default(engine, rubyVersion) {
+  if (engine === 'ruby') {
+    return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 2.7
+  } else if (engine === 'truffleruby') {
+    return isHeadVersion(rubyVersion)
+  } else {
+    return false
+  }
+}
+
+export function floatVersion(rubyVersion) {
+  const match = rubyVersion.match(/^\d+\.\d+/)
+  if (match) {
+    return parseFloat(match[0])
+  } else {
+    return 0.0
+  }
+}
+
 export async function hashFile(file) {
   // See https://github.com/actions/runner/blob/master/src/Misc/expressionFunc/hashFiles/src/hashFiles.ts
   const hash = crypto.createHash('sha256')
diff --git a/dist/index.js b/dist/index.js
index ed5e00c..c083475 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -32114,6 +32114,8 @@ __webpack_require__.r(__webpack_exports__);
 /* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "measure", function() { return measure; });
 /* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "isHeadVersion", function() { return isHeadVersion; });
 /* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "isStableVersion", function() { return isStableVersion; });
+/* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "isBundler2Default", function() { return isBundler2Default; });
+/* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "floatVersion", function() { return floatVersion; });
 /* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "hashFile", function() { return hashFile; });
 /* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "getVirtualEnvironmentName", function() { return getVirtualEnvironmentName; });
 /* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "shouldUseToolCache", function() { return shouldUseToolCache; });
@@ -32163,6 +32165,25 @@ function isStableVersion(rubyVersion) {
   return /^\d+(\.\d+)*$/.test(rubyVersion)
 }
 
+function isBundler2Default(engine, rubyVersion) {
+  if (engine === 'ruby') {
+    return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 2.7
+  } else if (engine === 'truffleruby') {
+    return isHeadVersion(rubyVersion)
+  } else {
+    return false
+  }
+}
+
+function floatVersion(rubyVersion) {
+  const match = rubyVersion.match(/^\d+\.\d+/)
+  if (match) {
+    return parseFloat(match[0])
+  } else {
+    return 0.0
+  }
+}
+
 async function hashFile(file) {
   // See https://github.com/actions/runner/blob/master/src/Misc/expressionFunc/hashFiles/src/hashFiles.ts
   const hash = crypto.createHash('sha256')
@@ -51416,7 +51437,7 @@ async function installBundler(bundlerVersionInput, lockFile, platform, rubyPrefi
     bundlerVersion = '1'
   }
 
-  if ((engine === 'ruby' || engine === 'truffleruby') && common.isHeadVersion(rubyVersion) && bundlerVersion === '2') {
+  if (common.isHeadVersion(rubyVersion) && common.isBundler2Default(engine, rubyVersion) && bundlerVersion === '2') {
     console.log(`Using Bundler 2 shipped with ${engine}-${rubyVersion}`)
   } else if (engine === 'truffleruby' && !common.isHeadVersion(rubyVersion) && bundlerVersion === '1') {
     console.log(`Using Bundler 1 shipped with ${engine}`)
@@ -51434,20 +51455,25 @@ async function bundleInstall(gemfile, lockFile, platform, engine, rubyVersion, b
     return false
   }
 
-  // Before the lockfile exists, we need to specify which Bundler version to use explicitly
-  const optionsWithBundlerVersion = { env: { ...process.env, BUNDLER_VERSION: bundlerVersion } }
+  let envOptions = {}
+  if (bundlerVersion.startsWith('1') && common.isBundler2Default(engine, rubyVersion)) {
+    // If Bundler 1 is specified on Rubies which ship with Bundler 2,
+    // we need to specify which Bundler version to use explicitly until the lockfile exists.
+    console.log(`Setting BUNDLER_VERSION=${bundlerVersion} for "bundle config|lock" commands below to ensure Bundler 1 is used`)
+    envOptions = { env: { ...process.env, BUNDLER_VERSION: bundlerVersion } }
+  }
 
   // config
   const path = 'vendor/bundle'
 
-  await exec.exec('bundle', ['config', '--local', 'path', path], optionsWithBundlerVersion)
+  await exec.exec('bundle', ['config', '--local', 'path', path], envOptions)
 
   if (fs.existsSync(lockFile)) {
-    await exec.exec('bundle', ['config', '--local', 'deployment', 'true'], optionsWithBundlerVersion)
+    await exec.exec('bundle', ['config', '--local', 'deployment', 'true'], envOptions)
   } else {
     // Generate the lockfile so we can use it to compute the cache key.
     // This will also automatically pick up the latest gem versions compatible with the Gemfile.
-    await exec.exec('bundle', ['lock'], optionsWithBundlerVersion)
+    await exec.exec('bundle', ['lock'], envOptions)
   }
 
   // cache key
diff --git a/index.js b/index.js
index 7d0e58a..5c84491 100644
--- a/index.js
+++ b/index.js
@@ -222,7 +222,7 @@ async function installBundler(bundlerVersionInput, lockFile, platform, rubyPrefi
     bundlerVersion = '1'
   }
 
-  if ((engine === 'ruby' || engine === 'truffleruby') && common.isHeadVersion(rubyVersion) && bundlerVersion === '2') {
+  if (common.isHeadVersion(rubyVersion) && common.isBundler2Default(engine, rubyVersion) && bundlerVersion === '2') {
     console.log(`Using Bundler 2 shipped with ${engine}-${rubyVersion}`)
   } else if (engine === 'truffleruby' && !common.isHeadVersion(rubyVersion) && bundlerVersion === '1') {
     console.log(`Using Bundler 1 shipped with ${engine}`)
@@ -240,20 +240,25 @@ async function bundleInstall(gemfile, lockFile, platform, engine, rubyVersion, b
     return false
   }
 
-  // Before the lockfile exists, we need to specify which Bundler version to use explicitly
-  const optionsWithBundlerVersion = { env: { ...process.env, BUNDLER_VERSION: bundlerVersion } }
+  let envOptions = {}
+  if (bundlerVersion.startsWith('1') && common.isBundler2Default(engine, rubyVersion)) {
+    // If Bundler 1 is specified on Rubies which ship with Bundler 2,
+    // we need to specify which Bundler version to use explicitly until the lockfile exists.
+    console.log(`Setting BUNDLER_VERSION=${bundlerVersion} for "bundle config|lock" commands below to ensure Bundler 1 is used`)
+    envOptions = { env: { ...process.env, BUNDLER_VERSION: bundlerVersion } }
+  }
 
   // config
   const path = 'vendor/bundle'
 
-  await exec.exec('bundle', ['config', '--local', 'path', path], optionsWithBundlerVersion)
+  await exec.exec('bundle', ['config', '--local', 'path', path], envOptions)
 
   if (fs.existsSync(lockFile)) {
-    await exec.exec('bundle', ['config', '--local', 'deployment', 'true'], optionsWithBundlerVersion)
+    await exec.exec('bundle', ['config', '--local', 'deployment', 'true'], envOptions)
   } else {
     // Generate the lockfile so we can use it to compute the cache key.
     // This will also automatically pick up the latest gem versions compatible with the Gemfile.
-    await exec.exec('bundle', ['lock'], optionsWithBundlerVersion)
+    await exec.exec('bundle', ['lock'], envOptions)
   }
 
   // cache key