diff --git a/aws_lambda_builders/workflows/nodejs_npm_esbuild/esbuild.py b/aws_lambda_builders/workflows/nodejs_npm_esbuild/esbuild.py
index 209727720..09525bf9b 100644
--- a/aws_lambda_builders/workflows/nodejs_npm_esbuild/esbuild.py
+++ b/aws_lambda_builders/workflows/nodejs_npm_esbuild/esbuild.py
@@ -120,6 +120,7 @@ def run(self, args, cwd=None):
 SUPPORTED_ESBUILD_APIS_MULTI_VALUE = [
     "external",
     "loader",
+    "out_extension",
 ]
 
 
diff --git a/tests/integration/workflows/nodejs_npm_esbuild/test_nodejs_npm_with_esbuild.py b/tests/integration/workflows/nodejs_npm_esbuild/test_nodejs_npm_with_esbuild.py
index b6b7e5dca..a9739841b 100644
--- a/tests/integration/workflows/nodejs_npm_esbuild/test_nodejs_npm_with_esbuild.py
+++ b/tests/integration/workflows/nodejs_npm_esbuild/test_nodejs_npm_with_esbuild.py
@@ -3,7 +3,6 @@
 import tempfile
 from pathlib import Path
 from unittest import TestCase
-from unittest.mock import patch
 
 from aws_lambda_builders.builder import LambdaBuilder
 from aws_lambda_builders.exceptions import WorkflowFailedError
@@ -388,3 +387,23 @@ def test_includes_sourcemap_if_requested(self, runtime):
         expected_files = {"included.js", "included.js.map"}
         output_files = set(os.listdir(self.artifacts_dir))
         self.assertEqual(expected_files, output_files)
+
+    @parameterized.expand([("nodejs12.x",), ("nodejs14.x",), ("nodejs16.x",), ("nodejs18.x",)])
+    def test_esbuild_produces_mjs_output_files(self, runtime):
+        source_dir = os.path.join(self.TEST_DATA_FOLDER, "with-deps-esbuild")
+        options = {"entry_points": ["included.js"], "sourcemap": True, "out_extension": [".js=.mjs"]}
+
+        self.builder.build(
+            source_dir,
+            self.artifacts_dir,
+            self.scratch_dir,
+            os.path.join(source_dir, "package.json"),
+            runtime=runtime,
+            options=options,
+            experimental_flags=[],
+            executable_search_paths=[self.binpath],
+        )
+
+        expected_files = {"included.mjs", "included.mjs.map"}
+        output_files = set(os.listdir(self.artifacts_dir))
+        self.assertEqual(expected_files, output_files)
diff --git a/tests/unit/workflows/nodejs_npm_esbuild/test_esbuild.py b/tests/unit/workflows/nodejs_npm_esbuild/test_esbuild.py
index f38b81b8f..f62fc3e54 100644
--- a/tests/unit/workflows/nodejs_npm_esbuild/test_esbuild.py
+++ b/tests/unit/workflows/nodejs_npm_esbuild/test_esbuild.py
@@ -200,6 +200,7 @@ def test_builds_args_from_config(self, osutils_mock):
             "target": "node14",
             "loader": [".proto=text", ".json=js"],
             "external": ["aws-sdk", "axios"],
+            "out_extension": [".js=.mjs"],
             "main_fields": "module,main",
         }
 
@@ -219,6 +220,7 @@ def test_builds_args_from_config(self, osutils_mock):
                 "--external:axios",
                 "--loader:.proto=text",
                 "--loader:.json=js",
+                "--out-extension:.js=.mjs",
             ],
         )