diff --git a/tests/admin_pages/test_workflow.py b/tests/admin_pages/test_workflow.py
index 1a886aa9d..c63e8ec55 100644
--- a/tests/admin_pages/test_workflow.py
+++ b/tests/admin_pages/test_workflow.py
@@ -1,6 +1,7 @@
 import io
 import os
 import re
+import uuid
 import xml.etree.ElementTree as ET
 
 import pytest
@@ -1793,36 +1794,39 @@ def test_workflows_variables(pub):
 
     # check it's been saved correctly
     assert 'foobar' in resp.text
-    assert len(Workflow.get(1).variables_formdef.fields) == 1
-    assert Workflow.get(1).variables_formdef.fields[0].key == 'string'
-    assert Workflow.get(1).variables_formdef.fields[0].label == 'foobar'
+    workflow = Workflow.get(1)
+    assert len(workflow.variables_formdef.fields) == 1
+    assert workflow.variables_formdef.fields[0].key == 'string'
+    assert workflow.variables_formdef.fields[0].label == 'foobar'
+    uuid.UUID(workflow.variables_formdef.fields[0].id)  # no ValueError
 
 
 def test_workflows_variables_edit(pub):
     test_workflows_variables(pub)
+    workflow = Workflow.get(1)
 
     app = login(get_app(pub))
     resp = app.get('/backoffice/workflows/1/')
     resp = resp.click(href='variables/', index=0)
     assert resp.location == 'http://example.net/backoffice/workflows/1/variables/fields/'
     resp = resp.follow()
-    resp = resp.click('Edit', href='1/')
+    resp = resp.click('Edit', href='%s/' % workflow.variables_formdef.fields[0].id)
     assert resp.forms[0]['varname$name'].value == 'foobar'
     assert 'varname$select' not in resp.forms[0].fields
 
-    workflow = Workflow.get(1)
     baz_status = workflow.add_status(name='baz')
     baz_status.add_action('displaymsg')
     workflow.store()
 
     resp = app.get('/backoffice/workflows/1/variables/fields/')
-    resp = resp.click('Edit', href='1/')
+    resp = resp.click('Edit', href='%s/' % workflow.variables_formdef.fields[0].id)
     assert 'varname$select' in resp.forms[0].fields
     resp.forms[0]['varname$select'].value = '1*1*message'
     resp = resp.forms[0].submit('submit')
 
-    assert Workflow.get(1).variables_formdef.fields[0].key == 'string'
-    assert Workflow.get(1).variables_formdef.fields[0].varname == '1*1*message'
+    workflow = Workflow.get(1)
+    assert workflow.variables_formdef.fields[0].key == 'string'
+    assert workflow.variables_formdef.fields[0].varname == '1*1*message'
 
 
 def test_workflows_variables_edit_with_all_action_types(pub):
@@ -1848,14 +1852,16 @@ def test_workflows_variables_edit_with_all_action_types(pub):
     assert resp.location == 'http://example.net/backoffice/workflows/1/variables/fields/'
     resp = resp.follow()
 
+    workflow = Workflow.get(1)
     resp = app.get('/backoffice/workflows/1/variables/fields/')
-    resp = resp.click('Edit', href='1/')
+    resp = resp.click('Edit', href='%s/' % workflow.variables_formdef.fields[0].id)
     assert 'varname$select' in resp.forms[0].fields
     resp.forms[0]['varname$name'].value = 'xxx'
     resp = resp.forms[0].submit('submit')
 
-    assert Workflow.get(1).variables_formdef.fields[0].key == 'string'
-    assert Workflow.get(1).variables_formdef.fields[0].varname == 'xxx'
+    workflow = Workflow.get(1)
+    assert workflow.variables_formdef.fields[0].key == 'string'
+    assert workflow.variables_formdef.fields[0].varname == 'xxx'
 
 
 def test_workflows_variables_delete(pub):
@@ -1932,7 +1938,7 @@ def test_workflows_variables_with_export_to_model_action(pub):
 
     app = login(get_app(pub))
     resp = app.get('/backoffice/workflows/1/variables/fields/')
-    resp = resp.click('Edit', href='1/')
+    resp = resp.click('Edit', href='%s/' % workflow.variables_formdef.fields[0].id)
 
 
 def test_workflows_export_to_model_in_status(pub):
@@ -1990,9 +1996,10 @@ def test_workflows_variables_replacement(pub):
     resp.forms[0]['label'] = 'foobar'
     resp.forms[0]['type'] = 'string'
     resp = resp.forms[0].submit().follow()
+    workflow = Workflow.get(1)
 
     # edit
-    resp = resp.click('Edit', href='1/')
+    resp = resp.click('Edit', href='%s/' % workflow.variables_formdef.fields[0].id)
     resp.form['varname$select'].value = '1*1*message'
     resp = resp.form.submit('submit').follow()
 
diff --git a/wcs/workflows.py b/wcs/workflows.py
index ee4d5ea41..d7828ce68 100644
--- a/wcs/workflows.py
+++ b/wcs/workflows.py
@@ -576,7 +576,6 @@ class WorkflowVariablesFieldsFormDef(FormDef):
             self.readonly = True
         if workflow.variables_formdef and workflow.variables_formdef.fields:
             self.fields = self.workflow.variables_formdef.fields
-            self.max_field_id = max(lax_int(x.id) for x in self.fields or [])
         else:
             self.fields = []
 
@@ -588,6 +587,9 @@ class WorkflowVariablesFieldsFormDef(FormDef):
         base_url = get_publisher().get_backoffice_url()
         return '%s/workflows/%s/variables/fields/' % (base_url, self.workflow.id)
 
+    def get_new_field_id(self):
+        return str(uuid.uuid4())
+
     def store(self, comment=None, *args, **kwargs):
         for field in self.fields:
             if hasattr(field, 'widget_class'):