diff --git a/juju/constraints.py b/juju/constraints.py
index 2574b6b08..3315feadc 100644
--- a/juju/constraints.py
+++ b/juju/constraints.py
@@ -54,7 +54,7 @@
     "zones",
     "allocate_public_ip"]
 
-LIST_KEYS = {'tags', 'spaces'}
+LIST_KEYS = {'tags', 'spaces', 'zones'}
 
 SNAKE1 = re.compile(r'(.)([A-Z][a-z]+)')
 SNAKE2 = re.compile('([a-z0-9])([A-Z])')
diff --git a/tests/unit/test_constraints.py b/tests/unit/test_constraints.py
index 03b2013f7..1fac2ccd6 100644
--- a/tests/unit/test_constraints.py
+++ b/tests/unit/test_constraints.py
@@ -60,7 +60,7 @@ def test_parse_constraints(self):
         self.assertEqual(
             _("mem=10G zones=bar,baz tags=tag1 spaces=space1,space2"),
             {"mem": 10 * 1024,
-             "zones": "bar,baz",
+             "zones": ["bar", "baz"],
              "tags": ["tag1"],
              "spaces": ["space1", "space2"]}
         )