diff --git a/README.md b/README.md
index cfcbfcc..f2cf36e 100644
--- a/README.md
+++ b/README.md
@@ -13,8 +13,8 @@ This Terraform module creates and uploads an AWS Lambda function and hides the u
 
 ## Requirements
 
-* Python
-* Linux/Unix
+* Python 2.7 or higher
+* Linux/Unix/Windows
 
 ## Usage
 
diff --git a/archive.tf b/archive.tf
index 071a0b3..9f5be61 100644
--- a/archive.tf
+++ b/archive.tf
@@ -1,7 +1,7 @@
 # Generates a filename for the zip archive based on the contents of the files
 # in source_path. The filename will change when the source code changes.
 data "external" "archive" {
-  program = ["${path.module}/hash.py"]
+  program = ["python", "${path.module}/hash.py"]
 
   query = {
     runtime     = "${var.runtime}"
@@ -26,7 +26,7 @@ resource "null_resource" "archive" {
 # deletes the Lambda function. If the file is rebuilt here, the build
 # output is unfortunately invisible.
 data "external" "built" {
-  program = ["${path.module}/built.py"]
+  program = ["python", "${path.module}/built.py"]
 
   query = {
     build_command = "${lookup(data.external.archive.result, "build_command")}"
diff --git a/build.py b/build.py
old mode 100755
new mode 100644
index e5e8385..6e1be00
--- a/build.py
+++ b/build.py
@@ -1,8 +1,5 @@
-#!/usr/bin/env python3
-#
 # Builds a zip file from the source_dir or source_file.
 # Installs dependencies with pip automatically.
-#
 
 import base64
 import json
@@ -15,15 +12,20 @@
 from contextlib import contextmanager
 
 
+@contextmanager
 def cd(path):
     """
     Changes the working directory.
 
     """
 
-    if os.getcwd() != path:
-        print('cd', path)
+    cwd = os.getcwd()
+    print('cd', path)
+    try:
         os.chdir(path)
+        yield
+    finally:
+        os.chdir(cwd)
 
 
 def format_command(command):
@@ -96,8 +98,12 @@ def create_zip_file(source_dir, target_file):
     target_dir = os.path.dirname(target_file)
     if not os.path.exists(target_dir):
         os.makedirs(target_dir)
-    cd(source_dir)
-    run('zip', '-r', target_file, '.')
+    target_base, _ = os.path.splitext(target_file)
+    shutil.make_archive(
+        target_base,
+        format='zip',
+        root_dir=source_dir,
+    )
 
 json_payload = bytes.decode(base64.b64decode(sys.argv[1]))
 query = json.loads(json_payload)
@@ -120,26 +126,26 @@ def create_zip_file(source_dir, target_file):
         source_files = [os.path.basename(source_path)]
 
     # Copy them into the temporary directory.
-    cd(source_dir)
-    for file_name in source_files:
-        target_path = os.path.join(temp_dir, file_name)
-        target_dir = os.path.dirname(target_path)
-        if not os.path.exists(target_dir):
-            print('mkdir -p {}'.format(target_dir))
-            os.makedirs(target_dir)
-        print('cp {} {}'.format(file_name, target_path))
-        shutil.copyfile(file_name, target_path)
+    with cd(source_dir):
+        for file_name in source_files:
+            target_path = os.path.join(temp_dir, file_name)
+            target_dir = os.path.dirname(target_path)
+            if not os.path.exists(target_dir):
+                print('mkdir -p {}'.format(target_dir))
+                os.makedirs(target_dir)
+            print('cp {} {}'.format(file_name, target_path))
+            shutil.copyfile(file_name, target_path)
 
     # Install dependencies into the temporary directory.
     if runtime.startswith('python'):
         requirements = os.path.join(temp_dir, 'requirements.txt')
         if os.path.exists(requirements):
-            cd(temp_dir)
-            if runtime.startswith('python3'):
-                pip_command = 'pip3'
-            else:
-                pip_command = 'pip2'
-            run(pip_command, 'install', '-r', 'requirements.txt', '-t', '.')
+            with cd(temp_dir):
+                if runtime.startswith('python3'):
+                    pip_command = 'pip3'
+                else:
+                    pip_command = 'pip2'
+                run(pip_command, 'install', '-r', 'requirements.txt', '-t', '.')
 
     # Zip up the temporary directory and write it to the target filename.
     # This will be used by the Lambda function as the source code package.
diff --git a/built.py b/built.py
old mode 100755
new mode 100644
index deb128f..6f96061
--- a/built.py
+++ b/built.py
@@ -1,4 +1,5 @@
-#!/usr/bin/env python3
+# Builds missing zip files included in the
+# Terraform state but missing from the disk.
 
 import json
 import os
diff --git a/hash.py b/hash.py
old mode 100755
new mode 100644
index 8e2beb4..1f9bf44
--- a/hash.py
+++ b/hash.py
@@ -1,10 +1,7 @@
-#!/usr/bin/env python3
-#
 # Generates a content hash of the source_path, which is used to determine if
 # the Lambda code has changed, ignoring file modification and access times.
 #
 # Outputs a filename and a command to run if the archive needs to be built.
-#
 
 import base64
 import datetime
@@ -145,7 +142,7 @@ def update_hash(hash_obj, file_root, file_path):
 )
 
 # Determine the command to run if Terraform wants to build a new archive.
-build_command = "{build_script} {build_data}".format(
+build_command = "python {build_script} {build_data}".format(
     build_script=os.path.join(current_dir, 'build.py'),
     build_data=bytes.decode(base64.b64encode(str.encode(
         json.dumps({
diff --git a/tests/python3-pip/lambda/__init__.py b/tests/python-versions/lambda/__init__.py
similarity index 100%
rename from tests/python3-pip/lambda/__init__.py
rename to tests/python-versions/lambda/__init__.py
diff --git a/tests/python3-pip/lambda/main.py b/tests/python-versions/lambda/main.py
similarity index 100%
rename from tests/python3-pip/lambda/main.py
rename to tests/python-versions/lambda/main.py
diff --git a/tests/python3-pip/lambda/requirements.txt b/tests/python-versions/lambda/requirements.txt
similarity index 100%
rename from tests/python3-pip/lambda/requirements.txt
rename to tests/python-versions/lambda/requirements.txt
diff --git a/tests/python3-pip/lambda/test_result/__init__.py b/tests/python-versions/lambda/test_result/__init__.py
similarity index 100%
rename from tests/python3-pip/lambda/test_result/__init__.py
rename to tests/python-versions/lambda/test_result/__init__.py
diff --git a/tests/python-versions/python2/.envrc b/tests/python-versions/python2/.envrc
new file mode 100644
index 0000000..7969e54
--- /dev/null
+++ b/tests/python-versions/python2/.envrc
@@ -0,0 +1 @@
+layout python2
diff --git a/tests/python-versions/python2/main.tf b/tests/python-versions/python2/main.tf
new file mode 100644
index 0000000..7e611c9
--- /dev/null
+++ b/tests/python-versions/python2/main.tf
@@ -0,0 +1,33 @@
+terraform {
+  backend "local" {
+    path = "terraform.tfstate"
+  }
+}
+
+provider "aws" {
+  region = "eu-west-1"
+}
+
+module "lambda_python2" {
+  source = "../../../"
+
+  function_name = "terraform-aws-lambda-test-python2-from-python2"
+  description   = "Test python2 runtime from python2 environment in terraform-aws-lambda"
+  handler       = "main.lambda_handler"
+  runtime       = "python2.7"
+  timeout       = 5
+
+  source_path = "${path.module}/../lambda"
+}
+
+module "lambda_python3" {
+  source = "../../../"
+
+  function_name = "terraform-aws-lambda-test-python3-from-python2"
+  description   = "Test python3 runtime from python2 environment in terraform-aws-lambda"
+  handler       = "main.lambda_handler"
+  runtime       = "python3.7"
+  timeout       = 5
+
+  source_path = "${path.module}/../lambda"
+}
diff --git a/tests/python-versions/python3/.envrc b/tests/python-versions/python3/.envrc
new file mode 100644
index 0000000..94840b3
--- /dev/null
+++ b/tests/python-versions/python3/.envrc
@@ -0,0 +1 @@
+layout python3
diff --git a/tests/python-versions/python3/main.tf b/tests/python-versions/python3/main.tf
new file mode 100644
index 0000000..39f36d7
--- /dev/null
+++ b/tests/python-versions/python3/main.tf
@@ -0,0 +1,33 @@
+terraform {
+  backend "local" {
+    path = "terraform.tfstate"
+  }
+}
+
+provider "aws" {
+  region = "eu-west-1"
+}
+
+module "lambda_python2" {
+  source = "../../../"
+
+  function_name = "terraform-aws-lambda-test-python2-from-python3"
+  description   = "Test python2 runtime from python3 environment in terraform-aws-lambda"
+  handler       = "main.lambda_handler"
+  runtime       = "python2.7"
+  timeout       = 5
+
+  source_path = "${path.module}/../lambda"
+}
+
+module "lambda_python3" {
+  source = "../../../"
+
+  function_name = "terraform-aws-lambda-test-python3-from-python3"
+  description   = "Test python3 runtime from python3 environment in terraform-aws-lambda"
+  handler       = "main.lambda_handler"
+  runtime       = "python3.7"
+  timeout       = 5
+
+  source_path = "${path.module}/../lambda"
+}
diff --git a/tests/python3-pip/main.tf b/tests/python3-pip/main.tf
deleted file mode 100644
index d82b955..0000000
--- a/tests/python3-pip/main.tf
+++ /dev/null
@@ -1,21 +0,0 @@
-terraform {
-  backend "local" {
-    path = "terraform.tfstate"
-  }
-}
-
-provider "aws" {
-  region = "eu-west-1"
-}
-
-module "lambda" {
-  source = "../../"
-
-  function_name = "terraform-aws-lambda-test-python3-pip"
-  description   = "Test python3 pip functionality in terraform-aws-lambda"
-  handler       = "main.lambda_handler"
-  runtime       = "python3.6"
-  timeout       = 30
-
-  source_path = "${path.module}/lambda"
-}