diff --git a/lower-constraints.txt b/lower-constraints.txt
index bf90e5460..e59c71a33 100644
--- a/lower-constraints.txt
+++ b/lower-constraints.txt
@@ -135,7 +135,7 @@ python-zaqarclient==1.0.0
 python-zunclient==3.4.0
 python-qinlingclient==1.0.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==5.1
 reno==2.5.0
 repoze.lru==0.7
 requests-mock==1.2.0
diff --git a/mistral/services/workflows.py b/mistral/services/workflows.py
index 1e00f6cdd..657a58dcd 100644
--- a/mistral/services/workflows.py
+++ b/mistral/services/workflows.py
@@ -208,4 +208,4 @@ def _cut_wf_definition_from_all(wfs_yaml, wf_name):
     return safe_yaml.dump({
         'version': wfs_yaml['version'],
         wf_name: wfs_yaml[wf_name]
-    })
+    }, sort_keys=False)
diff --git a/mistral/tests/unit/services/test_workflow_service.py b/mistral/tests/unit/services/test_workflow_service.py
index e12dda941..ee63d12fc 100644
--- a/mistral/tests/unit/services/test_workflow_service.py
+++ b/mistral/tests/unit/services/test_workflow_service.py
@@ -144,6 +144,23 @@ test_workflow:
 
 """
 
+WORKFLOWS_WITH_KEY_ORDER = """
+---
+version: '2.0'
+
+wf1:
+  tasks:
+    task1:
+      publish:
+        we: 1
+        dont_want: 2
+        to_be_sorted: 3
+wf2:
+  tasks:
+    task1:
+      action: std.noop
+"""
+
 
 class WorkflowServiceTest(base.DbTestCase):
     def test_create_workflows(self):
@@ -166,6 +183,23 @@ class WorkflowServiceTest(base.DbTestCase):
         self.assertEqual('wf2', wf2_spec.get_name())
         self.assertEqual('direct', wf2_spec.get_type())
 
+    def test_preserve_key_ordering_in_workflow_definition(self):
+        db_wfs = wf_service.create_workflows(WORKFLOWS_WITH_KEY_ORDER)
+
+        self.assertEqual(2, len(db_wfs))
+
+        wf1_db = self._assert_single_item(db_wfs, name='wf1')
+        wf1_def = wf1_db.definition
+        published_values = wf1_def.splitlines()[-3:]
+        wf1_publish = [
+            item.strip()
+            for item in published_values
+        ]
+        self.assertEqual(
+            ['we: 1', 'dont_want: 2', 'to_be_sorted: 3'],
+            wf1_publish
+        )
+
     def test_engine_commands_are_valid_task_names(self):
         for name in workflows.ENGINE_COMMANDS:
             wf_text = WORKFLOW_WITH_VAR_TASK_NAME.format(task_name=name)
diff --git a/requirements.txt b/requirements.txt
index 7cf24d0be..674472dfc 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -57,7 +57,7 @@ python-vitrageclient>=2.0.0 # Apache-2.0
 python-zunclient>=3.4.0 # Apache-2.0
 python-qinlingclient>=1.0.0 # Apache-2.0
 PyJWT>=1.5 # MIT
-PyYAML>=3.12 # MIT
+PyYAML>=5.1 # MIT
 requests>=2.14.2 # Apache-2.0
 tenacity>=5.0.1 # Apache-2.0
 six>=1.10.0 # MIT