diff --git a/manila/api/v2/share_network_subnets.py b/manila/api/v2/share_network_subnets.py
index d41bbeccf9..20d0819cd7 100644
--- a/manila/api/v2/share_network_subnets.py
+++ b/manila/api/v2/share_network_subnets.py
@@ -92,6 +92,15 @@ class ShareNetworkSubnetController(wsgi.Controller,
                 LOG.error(msg)
                 raise exc.HTTPConflict(explanation=msg)
 
+            share_groups = db_api.share_group_get_all_by_share_server(
+                context, share_server['id'])
+            if share_groups:
+                msg = _("Cannot delete share network subnet %(id)s, it has "
+                        "one or more share groups.") % {
+                            'id': share_network_subnet_id}
+                LOG.error(msg)
+                raise exc.HTTPConflict(explanation=msg)
+
         # NOTE(silvacarlose): Do not allow the deletion of any share server
         # if any of them has the flag is_auto_deletable = False
         if not self._all_share_servers_are_auto_deletable(
diff --git a/manila/db/sqlalchemy/models.py b/manila/db/sqlalchemy/models.py
index d418368138..9e166dfc55 100644
--- a/manila/db/sqlalchemy/models.py
+++ b/manila/db/sqlalchemy/models.py
@@ -1142,9 +1142,11 @@ class ShareServer(BASE, ManilaBase):
                     'ShareInstance.deleted == "False")')
 
     share_groups = orm.relationship(
-        "ShareGroup", backref='share_server', primaryjoin='and_('
-        'ShareServer.id == ShareGroup.share_server_id,'
-        'ShareGroup.deleted == "False")')
+        "ShareGroup",
+        backref='share_server',
+        primaryjoin='and_('
+                    'ShareServer.id == ShareGroup.share_server_id,'
+                    'ShareGroup.deleted == "False")')
 
     _backend_details = orm.relationship(
         "ShareServerBackendDetails",
diff --git a/releasenotes/notes/bug-2004212-prevent-subnet-deletion-when-group-exists-a35355feb1bf6848.yaml b/releasenotes/notes/bug-2004212-prevent-subnet-deletion-when-group-exists-a35355feb1bf6848.yaml
new file mode 100644
index 0000000000..a5e48a6bb5
--- /dev/null
+++ b/releasenotes/notes/bug-2004212-prevent-subnet-deletion-when-group-exists-a35355feb1bf6848.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed an issue that allowed share network subnets to be deleted when they
+    were still related to a share group. An exception will now be raised when
+    Manila identify such existing relationship. For more details, please refer
+    to `Launchpad Bug 2004212 <https://bugs.launchpad.net/manila/+bug/2004212>`_.