diff --git a/moto/redshift/models.py b/moto/redshift/models.py
index 9a5850faf..c8a4e3531 100644
--- a/moto/redshift/models.py
+++ b/moto/redshift/models.py
@@ -67,7 +67,7 @@ class Cluster(TaggableResourceMixin, BaseModel):
                  preferred_maintenance_window, cluster_parameter_group_name,
                  automated_snapshot_retention_period, port, cluster_version,
                  allow_version_upgrade, number_of_nodes, publicly_accessible,
-                 encrypted, region_name, tags=None, iam_roles_arn=[]):
+                 encrypted, region_name, tags=None, iam_roles_arn=None):
         super(Cluster, self).__init__(region_name, tags)
         self.redshift_backend = redshift_backend
         self.cluster_identifier = cluster_identifier
@@ -112,7 +112,7 @@ class Cluster(TaggableResourceMixin, BaseModel):
         else:
             self.number_of_nodes = 1
 
-        self.iam_roles_arn = iam_roles_arn
+        self.iam_roles_arn = iam_roles_arn or []
 
     @classmethod
     def create_from_cloudformation_json(cls, resource_name, cloudformation_json, region_name):
@@ -357,7 +357,7 @@ class Snapshot(TaggableResourceMixin, BaseModel):
 
     resource_type = 'snapshot'
 
-    def __init__(self, cluster, snapshot_identifier, region_name, tags=None, iam_roles_arn=[]):
+    def __init__(self, cluster, snapshot_identifier, region_name, tags=None, iam_roles_arn=None):
         super(Snapshot, self).__init__(region_name, tags)
         self.cluster = copy.copy(cluster)
         self.snapshot_identifier = snapshot_identifier
@@ -365,7 +365,7 @@ class Snapshot(TaggableResourceMixin, BaseModel):
         self.status = 'available'
         self.create_time = iso_8601_datetime_with_milliseconds(
             datetime.datetime.now())
-        self.iam_roles_arn = iam_roles_arn
+        self.iam_roles_arn = iam_roles_arn or []
 
     @property
     def resource_id(self):