diff --git a/aws_lambda_builders/workflows/ruby_bundler/bundler.py b/aws_lambda_builders/workflows/ruby_bundler/bundler.py
index 33405f233..fecee69a9 100644
--- a/aws_lambda_builders/workflows/ruby_bundler/bundler.py
+++ b/aws_lambda_builders/workflows/ruby_bundler/bundler.py
@@ -48,9 +48,10 @@ def run(self, args, cwd=None):
 
         p = self.osutils.popen(invoke_bundler, stdout=self.osutils.pipe, stderr=self.osutils.pipe, cwd=cwd)
 
-        out, err = p.communicate()
+        out, _ = p.communicate()
 
         if p.returncode != 0:
-            raise BundlerExecutionError(message=err.decode("utf8").strip())
+            # Bundler has relevant information in stdout, not stderr.
+            raise BundlerExecutionError(message=out.decode("utf8").strip())
 
         return out.decode("utf8").strip()
diff --git a/tests/unit/workflows/ruby_bundler/test_bundler.py b/tests/unit/workflows/ruby_bundler/test_bundler.py
index 7a83af11a..fb8ab4612 100644
--- a/tests/unit/workflows/ruby_bundler/test_bundler.py
+++ b/tests/unit/workflows/ruby_bundler/test_bundler.py
@@ -58,7 +58,7 @@ def test_returns_popen_out_decoded_if_retcode_is_0(self):
 
     def test_raises_BundlerExecutionError_with_err_text_if_retcode_is_not_0(self):
         self.popen.returncode = 1
-        self.popen.err = b"some error text\n\n"
+        self.popen.out = b"some error text\n\n"
         with self.assertRaises(BundlerExecutionError) as raised:
             self.under_test.run(["install", "--without", "development", "test"])
         self.assertEqual(raised.exception.args[0], "Bundler Failed: some error text")