diff --git a/apidoc/introduction.md b/apidoc/introduction.md
index 1c543a29..ecbc03cc 100644
--- a/apidoc/introduction.md
+++ b/apidoc/introduction.md
@@ -23,6 +23,10 @@ Example:
 
     5a8d1c25bc2d41001927a265
 
+## Parameters
+
+Only if noted otherwise, all requests assume the payload encoded as JSON with `Content-type: application/json` header. Parameters prepended with a colon (`:`) are parameters which should be specified through the URL.
+
 ## Source code and Licenses
 
 You can find the whole source code of the API at GitHub in the [sensebox/openSenseMap-API](https://github.com/sensebox/openSenseMap-API) repository. You can obtain the code under the MIT License.
diff --git a/packages/api/lib/controllers/usersController.js b/packages/api/lib/controllers/usersController.js
index 1e5196ad..6c872aae 100644
--- a/packages/api/lib/controllers/usersController.js
+++ b/packages/api/lib/controllers/usersController.js
@@ -66,7 +66,7 @@ const registerUser = async function registerUser (req, res, next) {
 /**
  * @api {post} /users/sign-in Sign in
  * @apiName sign-in
- * @apiDescription Sign in using email or name and password. The response contains a valid JSON Web Token
+ * @apiDescription Sign in using email or name and password. The response contains a valid JSON Web Token. Always use `application/json` as content-type.
  * @apiGroup Users
  * @apiParam {String} email the email or name of the user
  * @apiParam {String} password the password of the user