diff --git a/src/rollup/index.ts b/src/rollup/index.ts
index 2960d43160f..746ba9f7517 100644
--- a/src/rollup/index.ts
+++ b/src/rollup/index.ts
@@ -272,6 +272,16 @@ export default async function rollup(rawInputOptions: GenericConfigObject): Prom
 			throw error;
 		}
 		await graph.pluginDriver.hookSeq('generateBundle', [outputOptions, outputBundle, isWrite]);
+		for (const key of Object.keys(outputBundle)) {
+			const file = outputBundle[key] as any;
+			if (!file.type) {
+				graph.warnDeprecation(
+					'A plugin is directly adding properties to the bundle object in the "generateBundle" hook. This is deprecated and will be removed in a future Rollup version, please use "this.emitAsset" instead.',
+					false
+				);
+				file.type = 'asset';
+			}
+		}
 		graph.pluginDriver.finaliseAssets();
 
 		timeEnd('GENERATE', 1);
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_config.js b/test/form/samples/deprecated/emit-asset-hacky/_config.js
new file mode 100644
index 00000000000..d40ed2b503a
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_config.js
@@ -0,0 +1,16 @@
+module.exports = {
+	description: 'supports emitting assets in a hacky way by editing the bundle object',
+	options: {
+		strictDeprecations: false,
+		plugins: {
+			generateBundle(options, outputBundle) {
+				const file = {
+					fileName: 'my-hacky-asset.txt',
+					isAsset: true,
+					source: 'My Hacky Source'
+				};
+				outputBundle[file.fileName] = file;
+			}
+		}
+	}
+};
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_expected/amd.js b/test/form/samples/deprecated/emit-asset-hacky/_expected/amd.js
new file mode 100644
index 00000000000..126aa22ee83
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_expected/amd.js
@@ -0,0 +1,5 @@
+define(function () { 'use strict';
+
+	console.log('main');
+
+});
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_expected/cjs.js b/test/form/samples/deprecated/emit-asset-hacky/_expected/cjs.js
new file mode 100644
index 00000000000..d0ed06d8c90
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_expected/cjs.js
@@ -0,0 +1,3 @@
+'use strict';
+
+console.log('main');
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_expected/es.js b/test/form/samples/deprecated/emit-asset-hacky/_expected/es.js
new file mode 100644
index 00000000000..c0b933d7b56
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_expected/es.js
@@ -0,0 +1 @@
+console.log('main');
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_expected/iife.js b/test/form/samples/deprecated/emit-asset-hacky/_expected/iife.js
new file mode 100644
index 00000000000..d283cbce8ba
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_expected/iife.js
@@ -0,0 +1,6 @@
+(function () {
+	'use strict';
+
+	console.log('main');
+
+}());
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_expected/my-hacky-asset.txt b/test/form/samples/deprecated/emit-asset-hacky/_expected/my-hacky-asset.txt
new file mode 100644
index 00000000000..61db1bb6537
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_expected/my-hacky-asset.txt
@@ -0,0 +1 @@
+My Hacky Source
\ No newline at end of file
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_expected/system.js b/test/form/samples/deprecated/emit-asset-hacky/_expected/system.js
new file mode 100644
index 00000000000..c83499bc2d4
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_expected/system.js
@@ -0,0 +1,10 @@
+System.register([], function () {
+	'use strict';
+	return {
+		execute: function () {
+
+			console.log('main');
+
+		}
+	};
+});
diff --git a/test/form/samples/deprecated/emit-asset-hacky/_expected/umd.js b/test/form/samples/deprecated/emit-asset-hacky/_expected/umd.js
new file mode 100644
index 00000000000..4768f1d9737
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/_expected/umd.js
@@ -0,0 +1,8 @@
+(function (factory) {
+	typeof define === 'function' && define.amd ? define(factory) :
+	factory();
+}(function () { 'use strict';
+
+	console.log('main');
+
+}));
diff --git a/test/form/samples/deprecated/emit-asset-hacky/main.js b/test/form/samples/deprecated/emit-asset-hacky/main.js
new file mode 100644
index 00000000000..c0b933d7b56
--- /dev/null
+++ b/test/form/samples/deprecated/emit-asset-hacky/main.js
@@ -0,0 +1 @@
+console.log('main');