diff --git a/package.json b/package.json
index 883147c..62cbdc7 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,7 @@
   },
   "peerDependencies": {
     "webpack": "^2 || ^3 || ^4",
-    "html-webpack-plugin": "^2 || ^3"
+    "html-webpack-plugin": "^2 || ^3 || ^4"
   },
   "devDependencies": {
     "codecov": "^3.1.0",
diff --git a/plugin.js b/plugin.js
index 4ba9296..71fef80 100644
--- a/plugin.js
+++ b/plugin.js
@@ -183,10 +183,20 @@ class CspHtmlWebpackPlugin {
   apply(compiler) {
     if (compiler.hooks) {
       compiler.hooks.compilation.tap('CspHtmlWebpackPlugin', compilation => {
-        compilation.hooks.htmlWebpackPluginAfterHtmlProcessing.tapAsync(
-          'CspHtmlWebpackPlugin',
-          this.processCsp.bind(this)
-        );
+        // HtmlWebPackPlugin 3.x
+        if (compilation.hooks.htmlWebpackPluginAfterHtmlProcessing) {
+          compilation.hooks.htmlWebpackPluginAfterHtmlProcessing.tapAsync(
+            'CspHtmlWebpackPlugin',
+            this.processCsp.bind(this)
+          );
+        } else {
+          // HtmlWebPackPlugin 4.x
+          const HtmlWebpackPlugin = require('html-webpack-plugin'); // eslint-disable-line global-require
+          HtmlWebpackPlugin.getHooks(compilation).beforeEmit.tapAsync(
+            'CspHtmlWebpackPlugin',
+            this.processCsp.bind(this)
+          );
+        }
       });
     } else {
       compiler.plugin('compilation', compilation => {