diff --git a/README.md b/README.md
index af28558..8ce6eac 100644
--- a/README.md
+++ b/README.md
@@ -89,3 +89,7 @@ By default, the object returned by configuer is frozen. Since it is also flat,
 the object is completely immutable. The `mutable` option makes configeur return
 an unfrozen object. This is not recommended in general, but may be useful for
 testing purposes.
+
+### `env`
+
+If you prefer to pass an environment object in manually, use this field.
diff --git a/index.d.ts b/index.d.ts
index 6cae534..b4213ed 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -13,6 +13,7 @@ type Parser = [string, (string) => any];
 interface Options {
   parsers?: Parser[],
   mutable?: Boolean
+  env?: Object
 }
 
 export default function configeur(environment: Environment, options?: Options): Object;
diff --git a/index.js b/index.js
index 4bcce55..92d9dc1 100644
--- a/index.js
+++ b/index.js
@@ -4,7 +4,7 @@ const processConfig = require('./lib/processConfig');
 const makeParsers = require('./lib/makeParsers');
 
 module.exports = function configeur(schema, options = {}) {
-  return processConfig(schema, process.env, makeParsers(options.parsers), options.mutable);
+  return processConfig(schema, options.env || process.env, makeParsers(options.parsers), options.mutable);
 };
 
 module.exports.default = module.exports;
diff --git a/test/index.test.js b/test/index.test.js
index 3484af0..65f8b18 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -48,8 +48,25 @@ describe('configeur', () => {
   });
 
   it('passes the schema, the environment, and the parsers to processConfig', () => {
-    configeur('fakeSchema', { parsers: 'fake-custom-parsers', mutable: 'is-mutable' });
+    configeur('fakeSchema', {
+      parsers: 'fake-custom-parsers',
+      mutable: 'is-mutable'
+    });
+
+    assert.deepEqual(processConfigStub.args, [
+      ['fakeSchema', { AN_ARG: 'argValue' }, 'fakeParsers', 'is-mutable']
+    ]);
+  });
+
+  it('uses the optional env field to override process.env', () => {
+    configeur('fakeSchema', {
+      parsers: 'fake-custom-parsers',
+      mutable: 'is-mutable',
+      env: { A_DIFFERENT_ARG: 'differentValue' }
+    });
 
-    assert.deepEqual(processConfigStub.args, [['fakeSchema', { AN_ARG: 'argValue' }, 'fakeParsers', 'is-mutable']]);
+    assert.deepEqual(processConfigStub.args, [
+      ['fakeSchema', { A_DIFFERENT_ARG: 'differentValue' }, 'fakeParsers', 'is-mutable']
+    ]);
   });
 });