diff --git a/versions/3.1.0.md b/versions/3.1.0.md
index ac68e58d8d..3b5d648947 100644
--- a/versions/3.1.0.md
+++ b/versions/3.1.0.md
@@ -75,6 +75,8 @@ Path templating refers to the usage of template expressions, delimited by curly
 
 Each template expression in the path MUST correspond to a path parameter that is included in the [Path Item](#path-item-object) itself and/or in each of the Path Item's [Operations](#operation-object).
 
+The value for these path parameters MUST NOT contain any unescaped "generic syntax" characters described by [RFC3986](https://tools.ietf.org/html/rfc3986#section-3): forward slashes (`/`), question marks (`?`), or hashes (`#`).
+
 ##### <a name="mediaTypes"></a>Media Types
 Media type definitions are spread across several resources.
 The media type definitions SHOULD be in compliance with [RFC6838](https://tools.ietf.org/html/rfc6838).