diff --git a/neutron_lib/api/definitions/extraroute_atomic.py b/neutron_lib/api/definitions/extraroute_atomic.py
index 73f63b718..ed04237ec 100644
--- a/neutron_lib/api/definitions/extraroute_atomic.py
+++ b/neutron_lib/api/definitions/extraroute_atomic.py
@@ -27,12 +27,11 @@ RESOURCE_ATTRIBUTE_MAP = {
     l3.ROUTERS: {}
 }
 SUB_RESOURCE_ATTRIBUTE_MAP = None
-ACTION_MAP = {
-    l3.ROUTER: {
-        'add_extraroutes': 'PUT',
-        'remove_extraroutes': 'PUT',
-    }
-}
+ACTION_MAP = l3.ACTION_MAP
+ACTION_MAP[l3.ROUTER].update({
+    'add_extraroutes': 'PUT',
+    'remove_extraroutes': 'PUT',
+})
 REQUIRED_EXTENSIONS = [l3.ALIAS, extraroute.ALIAS]
 OPTIONAL_EXTENSIONS = []
 ACTION_STATUS = {}
diff --git a/releasenotes/notes/extraroute-atomic-apidef-additive-fb783d66c08618d4.yaml b/releasenotes/notes/extraroute-atomic-apidef-additive-fb783d66c08618d4.yaml
new file mode 100644
index 000000000..7aace3050
--- /dev/null
+++ b/releasenotes/notes/extraroute-atomic-apidef-additive-fb783d66c08618d4.yaml
@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    The ``extraroute-atomic`` api-def's ACTION_MAP is changed so we add the
+    new member actions (``add_extraroutes`` and ``remove_extraroutes``) while
+    we also keep the ``router`` extension's member actions
+    (``add_router_interface`` and ``remove_router_interface``).