diff --git a/lib/ChunkManifestPlugin.js b/lib/ChunkManifestPlugin.js
index d7f2e03..c70cc30 100644
--- a/lib/ChunkManifestPlugin.js
+++ b/lib/ChunkManifestPlugin.js
@@ -38,7 +38,13 @@ ChunkManifestPlugin.prototype.apply = function(compiler) {
         oldChunkFilename = this.outputOptions.chunkFilename;
         this.outputOptions.chunkFilename = "__CHUNK_MANIFEST__";
         // mark as asset for emitting
-        compilation.assets[manifestFilename] = new RawSource(JSON.stringify(chunkManifest));
+        var mergedAssets;
+        if (compilation.assets[manifestFilename]) {
+          mergedAssets = Object.assign({}, JSON.parse(compilation.assets[manifestFilename]._value), chunkManifest);
+        } else {
+          mergedAssets = chunkManifest;
+        }
+        compilation.assets[manifestFilename] = new RawSource(JSON.stringify(mergedAssets));
         chunk.files.push(manifestFilename);
       }