diff --git a/neutron/ipam/subnet_alloc.py b/neutron/ipam/subnet_alloc.py
index 49b6eda2ab5..fdcabcca861 100644
--- a/neutron/ipam/subnet_alloc.py
+++ b/neutron/ipam/subnet_alloc.py
@@ -38,9 +38,20 @@ class SubnetAllocator(driver.Pool):
         super(SubnetAllocator, self).__init__(subnetpool, context)
         self._sp_helper = SubnetPoolHelper()
 
+    def _lock_subnetpool(self):
+        """Lock subnetpool associated row.
+
+        This method disallows to allocate concurrently 2 subnets in the same
+        subnetpool, it's required to ensure non-overlapping cidrs in the same
+        subnetpool.
+        """
+        # FIXME(cbrandily): not working with Galera
+        (self._context.session.query(models_v2.SubnetPool.id).
+         filter_by(id=self._subnetpool['id']).
+         with_lockmode('update').first())
+
     def _get_allocated_cidrs(self):
-        query = self._context.session.query(
-            models_v2.Subnet).with_lockmode('update')
+        query = self._context.session.query(models_v2.Subnet)
         subnets = query.filter_by(subnetpool_id=self._subnetpool['id'])
         return (x.cidr for x in subnets)
 
@@ -62,8 +73,7 @@ class SubnetAllocator(driver.Pool):
         subnetpool_id = self._subnetpool['id']
         tenant_id = self._subnetpool['tenant_id']
         with self._context.session.begin(subtransactions=True):
-            qry = self._context.session.query(
-                 models_v2.Subnet).with_lockmode('update')
+            qry = self._context.session.query(models_v2.Subnet)
             allocations = qry.filter_by(subnetpool_id=subnetpool_id,
                                         tenant_id=tenant_id)
             value = 0
@@ -88,6 +98,7 @@ class SubnetAllocator(driver.Pool):
 
     def _allocate_any_subnet(self, request):
         with self._context.session.begin(subtransactions=True):
+            self._lock_subnetpool()
             self._check_subnetpool_tenant_quota(request.tenant_id,
                                                 request.prefixlen)
             prefix_pool = self._get_available_prefix_list()
@@ -111,6 +122,7 @@ class SubnetAllocator(driver.Pool):
 
     def _allocate_specific_subnet(self, request):
         with self._context.session.begin(subtransactions=True):
+            self._lock_subnetpool()
             self._check_subnetpool_tenant_quota(request.tenant_id,
                                                 request.prefixlen)
             cidr = request.subnet_cidr