diff --git a/api-ref/source/errors.inc b/api-ref/source/errors.inc
index 4419162c0..730017d89 100644
--- a/api-ref/source/errors.inc
+++ b/api-ref/source/errors.inc
@@ -65,5 +65,11 @@ The defined errors are:
    * - ``placement.resource_provider.not_found``
      - A resource provider mentioned in an operation involving multiple
        resource providers, such as :ref:`reshaper`, does not exist.
+   * - ``placement.query.duplicate_key``
+     - A request included multiple instances of a query parameter that may only
+       be specified once.
+   * - ``placement.query.bad_value``
+     - A value in a request conformed to the schema, but failed semantic
+       validation.
 
 .. _errors: https://specs.openstack.org/openstack/api-wg/guidelines/errors.html
diff --git a/placement/errors.py b/placement/errors.py
index 14d55c80a..67fb24b74 100644
--- a/placement/errors.py
+++ b/placement/errors.py
@@ -38,6 +38,7 @@ URI.
 # Do not change the string values. Once set, they are set.
 # Do not reuse string values. There should be only one symbol for any
 # value.
+# Don't forget to document new error codes in api-ref/source/errors.inc.
 DEFAULT = 'placement.undefined_code'
 INVENTORY_INUSE = 'placement.inventory.inuse'
 CONCURRENT_UPDATE = 'placement.concurrent_update'