diff --git a/src/server/ExpressHttpServer.ts b/src/server/ExpressHttpServer.ts
index 7c6433d87..3658ddf51 100644
--- a/src/server/ExpressHttpServer.ts
+++ b/src/server/ExpressHttpServer.ts
@@ -20,13 +20,15 @@ export class ExpressHttpServer {
       methods: [ 'GET', 'HEAD', 'OPTIONS', 'POST', 'PUT', 'PATCH', 'DELETE' ],
     }));
 
-    app.use(async(request, response): Promise<void> => {
+    app.use(async(request, response, done): Promise<void> => {
       try {
         await this.handler.handleSafe({ request, response });
       } catch (error) {
         const errMsg = `${error.name}: ${error.message}\n${error.stack}`;
         process.stderr.write(errMsg);
         response.status(500).contentType('text/plain').send(errMsg);
+      } finally {
+        done();
       }
     });
     return app.listen(port);
diff --git a/test/unit/server/ExpressHttpServer.test.ts b/test/unit/server/ExpressHttpServer.test.ts
index ee10f6fa5..eeb0ed78b 100644
--- a/test/unit/server/ExpressHttpServer.test.ts
+++ b/test/unit/server/ExpressHttpServer.test.ts
@@ -77,6 +77,13 @@ describe('ExpressHttpServer', (): void => {
     });
   });
 
+  it('returns a 404 when the handler does not do anything.', async(): Promise<void> => {
+    handler.handle = async(input): Promise<void> => {
+      expect(input).toBeDefined();
+    };
+    await request(server).get('/').expect(404);
+  });
+
   it('catches errors thrown by its handler.', async(): Promise<void> => {
     handler.handle = async(): Promise<void> => {
       throw new Error('dummyError');