diff --git a/moto/ecs/models.py b/moto/ecs/models.py
index bc847b32e..f5a928791 100644
--- a/moto/ecs/models.py
+++ b/moto/ecs/models.py
@@ -289,7 +289,7 @@ class ContainerInstance(BaseObject):
              'type': 'STRINGSET'}]
         self.container_instance_arn = "arn:aws:ecs:us-east-1:012345678910:container-instance/{0}".format(
             str(uuid.uuid1()))
-        self.pending_task_count = 0
+        self.pending_tasks_count = 0
         self.remaining_resources = [
             {'doubleValue': 0.0,
              'integerValue': 4096,
@@ -314,7 +314,7 @@ class ContainerInstance(BaseObject):
              'stringSetValue': [],
              'type': 'STRINGSET'}
         ]
-        self.running_task_count = 0
+        self.running_tasks_count = 0
         self.version_info = {
             'agentVersion': "1.0.0",
             'agentHash': '4023248',
@@ -737,7 +737,7 @@ class EC2ContainerServiceBackend(BaseBackend):
                         resource["stringSetValue"].remove(str(port))
                     else:
                         resource["stringSetValue"].append(str(port))
-        container_instance.running_task_count += resource_multiplier * 1
+        container_instance.running_tasks_count += resource_multiplier * 1
 
     def deregister_container_instance(self, cluster_str, container_instance_str, force):
         failures = []
@@ -748,11 +748,11 @@ class EC2ContainerServiceBackend(BaseBackend):
         container_instance = self.container_instances[cluster_name].get(container_instance_id)
         if container_instance is None:
             raise Exception("{0} is not a container id in the cluster")
-        if not force and container_instance.running_task_count > 0:
+        if not force and container_instance.running_tasks_count > 0:
             raise Exception("Found running tasks on the instance.")
         # Currently assume that people might want to do something based around deregistered instances
         # with tasks left running on them - but nothing if no tasks were running already
-        elif force and container_instance.running_task_count > 0:
+        elif force and container_instance.running_tasks_count > 0:
             if not self.container_instances.get('orphaned'):
                 self.container_instances['orphaned'] = {}
             self.container_instances['orphaned'][container_instance_id] = container_instance
diff --git a/tests/test_ecs/test_ecs_boto3.py b/tests/test_ecs/test_ecs_boto3.py
index 1cc147fc5..990057749 100644
--- a/tests/test_ecs/test_ecs_boto3.py
+++ b/tests/test_ecs/test_ecs_boto3.py
@@ -1210,6 +1210,7 @@ def test_resource_reservation_and_release():
     remaining_resources['MEMORY'].should.equal(registered_resources['MEMORY'] - 400)
     registered_resources['PORTS'].append('80')
     remaining_resources['PORTS'].should.equal(registered_resources['PORTS'])
+    container_instance_description['runningTasksCount'].should.equal(1)
     client.stop_task(
         cluster='test_ecs_cluster',
         task=run_response['tasks'][0].get('taskArn'),
@@ -1223,6 +1224,7 @@ def test_resource_reservation_and_release():
     remaining_resources['CPU'].should.equal(registered_resources['CPU'])
     remaining_resources['MEMORY'].should.equal(registered_resources['MEMORY'])
     remaining_resources['PORTS'].should.equal(registered_resources['PORTS'])
+    container_instance_description['runningTasksCount'].should.equal(0)
 
 
 @mock_ecs