diff --git a/placement-api-ref/source/resource_providers.inc b/placement-api-ref/source/resource_providers.inc
index 60bae1f5106f..29ab33a7213e 100644
--- a/placement-api-ref/source/resource_providers.inc
+++ b/placement-api-ref/source/resource_providers.inc
@@ -15,6 +15,12 @@ List an optionally filtered collection of resource providers.
 
 Normal Response Codes: 200
 
+Error response codes: badRequest(400)
+
+A `400 BadRequest` response code will be returned
+if a resource class specified in ``resources`` request parameter
+does not exist.
+
 Request
 -------