diff --git a/neutron/plugins/ml2/config.py b/neutron/plugins/ml2/config.py
index 8ea7cbd7004..4e2e43d8b0a 100644
--- a/neutron/plugins/ml2/config.py
+++ b/neutron/plugins/ml2/config.py
@@ -16,7 +16,6 @@
 from oslo_config import cfg
 
 from neutron._i18n import _
-from neutron.common import constants
 
 ml2_opts = [
     cfg.ListOpt('type_drivers',
@@ -40,7 +39,7 @@ ml2_opts = [
                        "entrypoints to be loaded from the "
                        "neutron.ml2.extension_drivers namespace. "
                        "For example: extension_drivers = port_security,qos")),
-    cfg.IntOpt('path_mtu', default=constants.DEFAULT_NETWORK_MTU,
+    cfg.IntOpt('path_mtu', default=0,
                help=_('Maximum size of an IP packet (MTU) that can traverse '
                       'the underlying physical network infrastructure without '
                       'fragmentation. For instances using a '
diff --git a/releasenotes/notes/path-mtu-back-to-zero-e4f9e8bdd8317ad4.yaml b/releasenotes/notes/path-mtu-back-to-zero-e4f9e8bdd8317ad4.yaml
new file mode 100644
index 00000000000..0815e71423b
--- /dev/null
+++ b/releasenotes/notes/path-mtu-back-to-zero-e4f9e8bdd8317ad4.yaml
@@ -0,0 +1,9 @@
+---
+upgrade:
+  - In case you rely on the default ML2 path_mtu value of 1500 to cap MTU used
+    for new network resources, please set it explicitly in your ml2_conf.ini
+    file.
+fixes:
+  - The default value for ML2 path_mtu option is changed from 1500 to 0,
+    effectively disabling its participation in network MTU calculation unless
+    it's overridden in the ml2_conf.ini configuration file.