diff --git a/spec/components/commons/query.yaml b/spec/components/commons/query.yaml
index 4b78ca3..f538d15 100644
--- a/spec/components/commons/query.yaml
+++ b/spec/components/commons/query.yaml
@@ -156,7 +156,7 @@ components:
         type: array
     flags:
       allowReserved: true
-      description: Various flags about properties of the tour (multiple selection allowed).
+      description: Various flags about properties of the tour (multiple selection allowed). Only the values listed in the Flags schema are accepted, matched exactly (case-sensitive). Requests containing any other value are rejected with a 400 response.
       examples:
         oneFlag:
           summary: Filter for private tours only.
diff --git a/spec/paths/tours.yaml b/spec/paths/tours.yaml
index c870002..ef6b200 100644
--- a/spec/paths/tours.yaml
+++ b/spec/paths/tours.yaml
@@ -45,7 +45,7 @@ paths:
                         items:
                           $ref: "../components/schema/tour.yaml#/components/schemas/Tour"
         400:
-          description: Missing or invalid parameters, e.g. a 'q' value that contains no letters or numbers or exceeds 150 characters.
+          description: Missing or invalid parameters, e.g. a 'q' value that contains no letters or numbers or exceeds 150 characters, or a 'flags[]' value that is not one of the supported flags.
         500:
           description: Server error