diff --git a/lib/ChunkManifestPlugin.js b/lib/ChunkManifestPlugin.js
index 4da72d0..e6bef03 100644
--- a/lib/ChunkManifestPlugin.js
+++ b/lib/ChunkManifestPlugin.js
@@ -58,8 +58,13 @@ ChunkManifestPlugin.prototype.apply = function(compiler) {
 
     if (inlineManifest){
       compilation.plugin("html-webpack-plugin-before-html-generation", function (data, callback) {
+        var manifestData = data;
         var manifestHtml = "<script>window." + manifestVariable + "=" + JSON.stringify(chunkManifest) + "</script>";
-        callback(null, data.assets[manifestVariable] = manifestHtml);
+
+        manifestData.assets = manifestData.assets || {};
+        manifestData.assets[manifestVariable] = manifestHtml;
+
+        callback(null, manifestData);
       });
     }
   });