diff --git a/src/middlewares/openapi.request.validator.ts b/src/middlewares/openapi.request.validator.ts
index 9d4b4f69..376ecf5e 100644
--- a/src/middlewares/openapi.request.validator.ts
+++ b/src/middlewares/openapi.request.validator.ts
@@ -49,7 +49,7 @@ export class RequestValidator {
 
     // cache middleware by combining method, path, and contentType
     // TODO contentType could have value not_provided
-    const contentType = extractContentType(req);
+    const contentType = extractContentType(req) || 'not_provided';
     const key = `${req.method}-${req.path}-${contentType}`;
 
     if (!this._middlewareCache[key]) {
@@ -184,11 +184,11 @@ export class RequestValidator {
     if (requestBody.content) {
       const content = requestBody.content[contentType];
       if (!content) {
-        throw validationError(
-          415,
-          path,
-          `unsupported media type ${contentType}`,
-        );
+        const msg =
+          contentType === 'not_provided'
+            ? 'media type not specified'
+            : `unsupported media type ${contentType}`;
+        throw validationError(415, path, msg);
       }
       return content.schema || {};
     }
diff --git a/src/middlewares/openapi.response.validator.ts b/src/middlewares/openapi.response.validator.ts
index a0c9536c..7ad6cc63 100644
--- a/src/middlewares/openapi.response.validator.ts
+++ b/src/middlewares/openapi.response.validator.ts
@@ -45,7 +45,7 @@ export class ResponseValidator {
       return this.buildValidators(responses);
     }
 
-    const contentType = extractContentType(req);
+    const contentType = extractContentType(req) || 'not_provided';
     const key = `${req.method}-${req.path}-${contentType}`;
 
     let validators = this.validatorsCache[key];
diff --git a/src/middlewares/util.ts b/src/middlewares/util.ts
index 84ab10a1..d5193e8d 100644
--- a/src/middlewares/util.ts
+++ b/src/middlewares/util.ts
@@ -3,8 +3,11 @@ import * as Ajv from 'ajv';
 import { Request } from 'express';
 import { ValidationError } from '../framework/types';
 
-export function extractContentType(req: Request): string {
-  let contentType = req.headers['content-type'] || 'not_provided';
+export function extractContentType(req: Request): string | null {
+  let contentType = req.headers['content-type'];
+  if (!contentType) {
+    return null;
+  }
   let end = contentType.indexOf(';');
   end = end === -1 ? contentType.length : end;
   if (contentType) {
@@ -43,7 +46,9 @@ export function validationError(
  * TODO - do this some other way
  * @param errors
  */
-export function augmentAjvErrors(errors: Ajv.ErrorObject[] = []): Ajv.ErrorObject[] {
+export function augmentAjvErrors(
+  errors: Ajv.ErrorObject[] = [],
+): Ajv.ErrorObject[] {
   errors.forEach(e => {
     if (e.keyword === 'enum') {
       const params: any = e.params;