diff --git a/mistral/services/expiration_policy.py b/mistral/services/expiration_policy.py
index 6a2d5cb0c..c30c7d90c 100644
--- a/mistral/services/expiration_policy.py
+++ b/mistral/services/expiration_policy.py
@@ -43,7 +43,7 @@ class ExecutionExpirationPolicy(periodic_task.PeriodicTasks):
         interval = CONF.execution_expiration_policy.evaluation_interval
         older_than = CONF.execution_expiration_policy.older_than
 
-        if (interval and older_than >= 1):
+        if (interval and older_than and older_than >= 1):
             _periodic_task = periodic_task.periodic_task(
                 spacing=interval * 60,
                 run_immediately=True
diff --git a/mistral/services/periodic.py b/mistral/services/periodic.py
index ed2066d27..a157cb8dd 100644
--- a/mistral/services/periodic.py
+++ b/mistral/services/periodic.py
@@ -51,7 +51,8 @@ class MistralPeriodicTasks(periodic_task.PeriodicTasks):
                     **t.workflow_params
                 )
             finally:
-                if t.remaining_executions > 0:
+                if (t.remaining_executions is not None and
+                   t.remaining_executions > 0):
                     t.remaining_executions -= 1
                 if t.remaining_executions == 0:
                     db_api_v2.delete_cron_trigger(t.name)
diff --git a/mistral/services/triggers.py b/mistral/services/triggers.py
index 158b9aea6..65d1fe54c 100644
--- a/mistral/services/triggers.py
+++ b/mistral/services/triggers.py
@@ -45,7 +45,7 @@ def validate_cron_trigger_input(pattern, first_time, count):
             raise exc.InvalidModelException(
                 'first_execution_time must be at least 1 second in the future.'
             )
-        if not pattern and count > 1:
+        if not pattern and count and count > 1:
             raise exc.InvalidModelException(
                 'Pattern must be provided if count is superior to 1.'
             )
diff --git a/mistral/workflow/with_items.py b/mistral/workflow/with_items.py
index 0e07021e3..33558aeb9 100644
--- a/mistral/workflow/with_items.py
+++ b/mistral/workflow/with_items.py
@@ -111,12 +111,13 @@ def get_indices_for_loop(task_ex):
 def decrease_capacity(task_ex, count):
     with_items_context = _get_context(task_ex)
 
-    if with_items_context[_CAPACITY] >= count:
-        with_items_context[_CAPACITY] -= count
-    elif with_items_context[_CAPACITY]:
-        raise exc.WorkflowException(
-            "Impossible to apply current with-items concurrency."
-        )
+    if with_items_context[_CAPACITY] is not None:
+        if with_items_context[_CAPACITY] >= count:
+            with_items_context[_CAPACITY] -= count
+        else:
+            raise exc.WorkflowException(
+                "Impossible to apply current with-items concurrency."
+            )
 
     task_ex.runtime_context.update({_WITH_ITEMS: with_items_context})