diff --git a/README.md b/README.md
index d847bb8..3f94ea1 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,10 @@ module.exports = {
 
 This webpack plugin accepts a single argument, a function to which returns the code to inject into the bundle.
 
+The function is called using the same context as the loader, so everything [here](https://webpack.js.org/api/loaders/#the-loader-context) applies.
+
+You can either return the raw content to load, or a `Promise` which resolves to the content, if you wish to be async.
+
 Though this could be used as a standalone plugin, you could also use it to create other webpack plugins, such as injecting code into the build based on a config file.
 
 Example:
diff --git a/src/webpack-inject-plugin.loader.js b/src/webpack-inject-plugin.loader.js
index 402f687..4bf4cea 100644
--- a/src/webpack-inject-plugin.loader.js
+++ b/src/webpack-inject-plugin.loader.js
@@ -11,5 +11,14 @@ export default function (source) {
     func = registry[options.id];
   }
 
-  return func(source);
+  const rtn = func.call(this, source);
+
+  if (rtn instanceof Promise) {
+    const callback = this.async();
+    rtn.then((result, err) => {
+      callback(err, result);
+    });
+  }
+
+  return rtn;
 }