diff --git a/HISTORY.rst b/HISTORY.rst
index 8705dee8e1..9cc9ca28e0 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -30,6 +30,8 @@
 * Fix index list API view. Add index create, delete, detail API tests.
   GitLab issue #564. Thanks to the Stéphane (@shoyu) for the report and debug
   information.
+* Validate the state completion value before saving. Thanks to Manoel Brunnen
+  (@mbru) for the report and debug information. GitLab issue #557.
 
 3.1.9 (2018-11-01)
 ==================
diff --git a/docs/releases/3.1.10.rst b/docs/releases/3.1.10.rst
index 0020a9a5a5..1b23b40c4d 100644
--- a/docs/releases/3.1.10.rst
+++ b/docs/releases/3.1.10.rst
@@ -156,6 +156,7 @@ Backward incompatible changes
 Bugs fixed or issues closed
 ---------------------------
 
+* :gitlab-issue:`557` Break workflows with invalid input
 * :gitlab-issue:`559` IndexTestCase.test_dual_level_dual_document_index failure
 * :gitlab-issue:`562` events.links.link_user_notifications_list should use
   reverse
diff --git a/mayan/apps/document_states/models.py b/mayan/apps/document_states/models.py
index e64979c6c8..d553c7201d 100644
--- a/mayan/apps/document_states/models.py
+++ b/mayan/apps/document_states/models.py
@@ -208,6 +208,19 @@ class WorkflowState(models.Model):
         ).distinct()
 
     def save(self, *args, **kwargs):
+        # Solve issue #557 "Break workflows with invalid input"
+        # without using a migration.
+        # Remove blank=True, remove this, and create a migration in the next
+        # minor version.
+
+        try:
+            self.completion = int(self.completion)
+        except (TypeError, ValueError):
+            self.completion = 0
+
+        #if not self.completion:
+        #    self.completion = 0
+
         if self.initial:
             self.workflow.states.all().update(initial=False)
         return super(WorkflowState, self).save(*args, **kwargs)
diff --git a/mayan/apps/document_states/tests/test_views.py b/mayan/apps/document_states/tests/test_views.py
index 45f31aaadf..3537a4f3a2 100644
--- a/mayan/apps/document_states/tests/test_views.py
+++ b/mayan/apps/document_states/tests/test_views.py
@@ -135,13 +135,17 @@ class DocumentStateStateViewTestCase(WorkflowTestMixin, GenericViewTestCase):
         super(DocumentStateStateViewTestCase, self).setUp()
         self.login_user()
 
-    def _request_workflow_state_create_view(self):
+    def _request_workflow_state_create_view(self, extra_data=None):
+        data = {
+            'label': TEST_WORKFLOW_STATE_LABEL,
+            'completion': TEST_WORKFLOW_STATE_COMPLETION,
+        }
+        if extra_data:
+            data.update(extra_data)
+
         return self.post(
             viewname='document_states:setup_workflow_state_create',
-            args=(self.workflow.pk,), data={
-                'label': TEST_WORKFLOW_STATE_LABEL,
-                'completion': TEST_WORKFLOW_STATE_COMPLETION,
-            }
+            args=(self.workflow.pk,), data=data
         )
 
     def test_create_workflow_state_no_access(self):
@@ -164,6 +168,23 @@ class DocumentStateStateViewTestCase(WorkflowTestMixin, GenericViewTestCase):
             TEST_WORKFLOW_STATE_COMPLETION
         )
 
+    def test_create_workflow_state_invalid_completion_with_access(self):
+        self._create_workflow()
+
+        self.grant_access(obj=self.workflow, permission=permission_workflow_edit)
+
+        response = self._request_workflow_state_create_view(
+            extra_data={'completion': ''}
+        )
+        self.assertEquals(response.status_code, 302)
+        self.assertEquals(WorkflowState.objects.count(), 1)
+        self.assertEquals(
+            WorkflowState.objects.all()[0].label, TEST_WORKFLOW_STATE_LABEL
+        )
+        self.assertEquals(
+            WorkflowState.objects.all()[0].completion, 0
+        )
+
     def _request_workflow_state_delete_view(self):
         return self.post(
             viewname='document_states:setup_workflow_state_delete',