diff --git a/package.json b/package.json
index af5c5f8..d4204d9 100644
--- a/package.json
+++ b/package.json
@@ -22,6 +22,7 @@
     "chalk": "^2.3.0",
     "cheerio": "^1.0.0-rc.2",
     "chokidar": "^1.7.0",
+    "devalue": "^1.0.1",
     "glob": "^7.1.2",
     "mkdirp": "^0.5.1",
     "node-fetch": "^1.7.3",
@@ -32,7 +33,6 @@
     "rimraf": "^2.6.2",
     "sade": "^1.4.0",
     "sander": "^0.6.0",
-    "serialize-javascript": "^1.4.0",
     "source-map-support": "^0.5.3",
     "tslib": "^1.9.0",
     "url-parse": "^1.2.0",
diff --git a/src/middleware/index.ts b/src/middleware/index.ts
index 0c95bbb..ebe0db3 100644
--- a/src/middleware/index.ts
+++ b/src/middleware/index.ts
@@ -3,7 +3,7 @@ import * as path from 'path';
 import { ClientRequest, ServerResponse } from 'http';
 import mkdirp from 'mkdirp';
 import rimraf from 'rimraf';
-import serialize from 'serialize-javascript';
+import devalue from 'devalue';
 import { lookup } from './mime';
 import { create_routes, templates, create_compilers } from 'sapper/core.js';
 import { dest, dev } from '../config';
@@ -331,7 +331,7 @@ function read_json(file: string) {
 
 function try_serialize(data: any) {
 	try {
-		return serialize(data);
+		return devalue(data);
 	} catch (err) {
 		return null;
 	}
diff --git a/test/app/routes/preload-values/custom-class.html b/test/app/routes/preload-values/custom-class.html
new file mode 100644
index 0000000..328e335
--- /dev/null
+++ b/test/app/routes/preload-values/custom-class.html
@@ -0,0 +1,17 @@
+<h1>{{foo.bar()}}</h1>
+
+<script>
+	export default {
+		preload() {
+			class Foo {
+				bar() {
+					return 42;
+				}
+			}
+
+			return {
+				foo: new Foo()
+			};
+		}
+	};
+</script>
\ No newline at end of file
diff --git a/test/app/routes/preload-values/set.html b/test/app/routes/preload-values/set.html
new file mode 100644
index 0000000..b8c0df1
--- /dev/null
+++ b/test/app/routes/preload-values/set.html
@@ -0,0 +1,11 @@
+<h1>{{set.has('x')}}</h1>
+
+<script>
+	export default {
+		preload() {
+			return {
+				set: new Set(['x'])
+			};
+		}
+	};
+</script>
\ No newline at end of file
diff --git a/test/common/test.js b/test/common/test.js
index 40d44a6..f825e84 100644
--- a/test/common/test.js
+++ b/test/common/test.js
@@ -487,6 +487,30 @@ function run(env) {
 						assert.equal(title, `I'm afraid I just blue myself`);
 					});
 			});
+
+			it('serializes Set objects returned from preload', () => {
+				return nightmare.goto(`${base}/preload-values/set`)
+					.page.title()
+					.then(title => {
+						assert.equal(title, 'true');
+						return nightmare.init().page.title();
+					})
+					.then(title => {
+						assert.equal(title, 'true');
+					});
+			});
+
+			it('bails on custom classes returned from preload', () => {
+				return nightmare.goto(`${base}/preload-values/custom-class`)
+					.page.title()
+					.then(title => {
+						assert.equal(title, '42');
+						return nightmare.init().page.title();
+					})
+					.then(title => {
+						assert.equal(title, '42');
+					});
+			});
 		});
 
 		describe('headers', () => {