diff --git a/.changes/next-release/bugfix-ecs-72910.json b/.changes/next-release/bugfix-ecs-72910.json
new file mode 100644
index 000000000000..e30e03f87828
--- /dev/null
+++ b/.changes/next-release/bugfix-ecs-72910.json
@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "ecs",
+  "description": "Fix `aws ecs deploy` falling back to the correct behavior for `--cluster \"\"` (an empty string, e.g. from an unset shell variable) the same way it already does when `--cluster` is omitted, instead of passing the empty string through to the ECS API"
+}
diff --git a/awscli/customizations/ecs/deploy.py b/awscli/customizations/ecs/deploy.py
index 8743ccb12ed4..1053d4e8c490 100644
--- a/awscli/customizations/ecs/deploy.py
+++ b/awscli/customizations/ecs/deploy.py
@@ -449,7 +449,7 @@ def __init__(self, session, parsed_args, parsed_globals, user_agent_extra):
     def get_service_details(self):
         cluster = self._args.cluster
 
-        if cluster is None or '':
+        if not cluster:
             cluster = 'default'
 
         try:
diff --git a/tests/unit/customizations/ecs/test_ecsclient.py b/tests/unit/customizations/ecs/test_ecsclient.py
index 4601d581ce0e..b4c33b7fc1ef 100644
--- a/tests/unit/customizations/ecs/test_ecsclient.py
+++ b/tests/unit/customizations/ecs/test_ecsclient.py
@@ -47,3 +47,40 @@ def test_client_config(self):
             create_args[1]['config'].user_agent_extra,
             expected_user_agent_extra,
         )
+
+    def _get_service_details_with_cluster(self, cluster):
+        args = Namespace(cluster=cluster, service='my-service')
+        test_client = ECSClient(
+            self.session, args, self.global_args, ECSDeploy.USER_AGENT_EXTRA
+        )
+        test_client._client = mock.Mock()
+        test_client._client.describe_services.return_value = {
+            'services': [
+                {
+                    'serviceArn': (
+                        'arn:aws:ecs:us-east-1:123456789012:service/my-service'
+                    ),
+                    'serviceName': 'my-service',
+                    'clusterArn': (
+                        'arn:aws:ecs:us-east-1:123456789012:cluster/default'
+                    ),
+                }
+            ]
+        }
+        test_client.get_service_details()
+        return test_client._client.describe_services.call_args[1]['cluster']
+
+    def test_get_service_details_defaults_cluster_when_not_specified(self):
+        used_cluster = self._get_service_details_with_cluster(None)
+        self.assertEqual(used_cluster, 'default')
+
+    def test_get_service_details_defaults_cluster_when_empty_string(self):
+        # A caller may pass an empty string for --cluster (e.g. by
+        # interpolating an unset shell variable), which should be treated
+        # the same as not specifying a cluster at all.
+        used_cluster = self._get_service_details_with_cluster('')
+        self.assertEqual(used_cluster, 'default')
+
+    def test_get_service_details_uses_specified_cluster(self):
+        used_cluster = self._get_service_details_with_cluster('my-cluster')
+        self.assertEqual(used_cluster, 'my-cluster')