diff --git a/dist/index.js b/dist/index.js
index 445d0de..ef17efe 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -51908,6 +51908,8 @@ function detectGemfiles() {
   const gemfilePath = process.env['BUNDLE_GEMFILE'] || 'Gemfile'
   if (fs.existsSync(gemfilePath)) {
     return [gemfilePath, `${gemfilePath}.lock`]
+  } else if (process.env['BUNDLE_GEMFILE']) {
+    throw new Error(`$BUNDLE_GEMFILE is set to ${gemfilePath} but does not exist`)
   }
 
   if (fs.existsSync("gems.rb")) {
diff --git a/index.js b/index.js
index 9a57fb4..7cfe526 100644
--- a/index.js
+++ b/index.js
@@ -80,6 +80,8 @@ function detectGemfiles() {
   const gemfilePath = process.env['BUNDLE_GEMFILE'] || 'Gemfile'
   if (fs.existsSync(gemfilePath)) {
     return [gemfilePath, `${gemfilePath}.lock`]
+  } else if (process.env['BUNDLE_GEMFILE']) {
+    throw new Error(`$BUNDLE_GEMFILE is set to ${gemfilePath} but does not exist`)
   }
 
   if (fs.existsSync("gems.rb")) {