diff --git a/src/openapi.validator.ts b/src/openapi.validator.ts
index 74f67a63..33eadbd2 100644
--- a/src/openapi.validator.ts
+++ b/src/openapi.validator.ts
@@ -1,5 +1,4 @@
 import ono from 'ono';
-import ajv = require('ajv');
 import * as express from 'express';
 import * as _uniq from 'lodash.uniq';
 import * as middlewares from './middlewares';
@@ -93,22 +92,37 @@ export class OpenApiValidator {
 
   installMiddleware(spec: Promise<Spec>): OpenApiRequestHandler[] {
     const middlewares: OpenApiRequestHandler[] = [];
-    const pContext = spec.then((spec) => {
-      const apiDoc = spec.apiDoc;
-      const ajvOpts = this.ajvOpts.preprocessor;
-      const resOpts = this.options.validateResponses as ValidateRequestOpts;
-      const sp = new SchemaPreprocessor(apiDoc, ajvOpts, resOpts).preProcess();
-      return {
-        context: new OpenApiContext(spec, this.options.ignorePaths),
-        responseApiDoc: sp.apiDocRes,
-      };
-    });
+    const pContext = spec
+      .then((spec) => {
+        const apiDoc = spec.apiDoc;
+        const ajvOpts = this.ajvOpts.preprocessor;
+        const resOpts = this.options.validateResponses as ValidateRequestOpts;
+        const sp = new SchemaPreprocessor(
+          apiDoc,
+          ajvOpts,
+          resOpts,
+        ).preProcess();
+        return {
+          context: new OpenApiContext(spec, this.options.ignorePaths),
+          responseApiDoc: sp.apiDocRes,
+          error: null,
+        };
+      })
+      .catch((e) => {
+        return {
+          context: null,
+          responseApiDoc: null,
+          error: e,
+        };
+      });
 
     let inited = false;
     // install path params
     middlewares.push((req, res, next) =>
       pContext
-        .then(({ context }) => {
+        .then(({ context, error }) => {
+          // Throw if any error occurred during spec load.
+          if (error) throw error;
           if (!inited) {
             // Would be nice to pass the current Router object here if the route
             // is attach to a Router and not the app.
diff --git a/test/invalid.apispec.spec.ts b/test/invalid.apispec.spec.ts
new file mode 100644
index 00000000..c6ae05b0
--- /dev/null
+++ b/test/invalid.apispec.spec.ts
@@ -0,0 +1,88 @@
+import * as express from 'express';
+import { Server } from 'http';
+import * as request from 'supertest';
+import * as OpenApiValidator from '../src';
+import { OpenAPIV3, OpenApiValidatorOpts } from '../src/framework/types';
+import { startServer } from './common/app.common';
+
+describe('invalid api spec', () => {
+  it('should propagate spec errors when validateApiSpec is true', async () => {
+    const apiSpec = createApiSpec();
+    const app = await createApp({
+      apiSpec,
+    });
+    await request(app).get('/dev/hello/echo').expect(500);
+    app.server.close();
+  });
+  it('should fail gracefully when validateApiSpec is false', async () => {
+    const apiSpec = createApiSpec();
+    const app = await createApp({
+      apiSpec,
+      validateApiSpec: false,
+    });
+    await request(app).get('/dev/hello/echo').expect(500);
+    app.server.close();
+  });
+});
+
+async function createApp(
+  opts: OpenApiValidatorOpts,
+): Promise<express.Express & { server?: Server }> {
+  const app = express();
+
+  app.use(OpenApiValidator.middleware(opts));
+  app.use(
+    express.Router().get('/dev/hello/echo', (req, res) => {
+      res.status(200).send(req.params.value);
+    }),
+  );
+
+  await startServer(app, 3001);
+  return app;
+}
+
+function createApiSpec(): OpenAPIV3.Document {
+  return <any>{
+    openapi: '3.0.3',
+    info: {
+      title: 'The API',
+      version: '1.0.0',
+      description: 'Welcome to the API.',
+    },
+    servers: [{ url: 'http://localhost:54321/v1', description: 'Running' }],
+    components: {
+      securitySchemes: {
+        AuthJWT: {
+          type: 'http',
+          scheme: 'bearer',
+          bearerFormat: 'JWT',
+          description:
+            'Enter a JSON Web Token (JWT) to be sent with each request in the HTTP **Authorization** header.',
+        },
+      },
+    },
+    security: [{ AuthJWT: [] }],
+    paths: {
+      '/dev/hello/echo': {
+        get: {
+          security: [],
+          summary: 'Responds with the request.',
+          description: '',
+          responses: { '200': { description: 'OK' } },
+          parameters: { q: 'string' }, // <-- THE INCORRECT BIT
+          tags: ['dev/hello'],
+        },
+      },
+      '/dev/hello/err': {
+        get: {
+          security: [],
+          summary: 'Responds with an error.',
+          description: '',
+          responses: { '500': { description: 'Error' } },
+          tags: ['dev/hello'],
+        },
+      },
+    },
+    tags: [{ name: 'dev/hello', description: 'API introduction' }],
+  };
+}