diff --git a/unit_tests/test_zaza_charm_lifecycle_deploy.py b/unit_tests/test_zaza_charm_lifecycle_deploy.py
index 4f38dd8..df84ab7 100644
--- a/unit_tests/test_zaza_charm_lifecycle_deploy.py
+++ b/unit_tests/test_zaza_charm_lifecycle_deploy.py
@@ -128,6 +128,23 @@ class TestCharmLifecycleDeploy(ut_utils.BaseTestCase):
             template_mock,
             '/tmp/special-dir/my_overlay.yaml')
 
+    def test_template_missing_required_variables(self):
+        self.patch_object(lc_deploy, 'get_template_overlay_context')
+        self.get_template_overlay_context.return_value = {}
+        self.patch_object(lc_deploy.sys, 'exit')
+        self.patch_object(lc_deploy.logging, 'error')
+        jinja2_env = lc_deploy.get_jinja2_env()
+        template = jinja2_env.from_string('{{required_variable}}')
+        m = mock.mock_open()
+        with mock.patch('zaza.charm_lifecycle.deploy.open', m, create=True):
+            lc_deploy.render_template(template, '/tmp/mybundle.yaml')
+        m.assert_called_once_with('/tmp/mybundle.yaml', 'w')
+        self.error.assert_called_once_with(
+            "Template error. You may be missing"
+            " a mandatory environment variable : "
+            "'required_variable' is undefined")
+        self.exit.assert_called_once_with(1)
+
     def test_render_overlay_no_template(self):
         self.patch_object(lc_deploy, 'get_template')
         self.get_template.return_value = None
diff --git a/zaza/charm_lifecycle/deploy.py b/zaza/charm_lifecycle/deploy.py
index 4264c67..8749251 100755
--- a/zaza/charm_lifecycle/deploy.py
+++ b/zaza/charm_lifecycle/deploy.py
@@ -118,7 +118,8 @@ def get_jinja2_env():
     """
     template_dir = get_overlay_template_dir()
     return jinja2.Environment(
-        loader=jinja2.FileSystemLoader(template_dir)
+        loader=jinja2.FileSystemLoader(template_dir),
+        undefined=jinja2.StrictUndefined
     )
 
 
@@ -158,10 +159,14 @@ def render_template(template, target_file):
     :param target_file: File name for rendered template
     :type target_file: str
     """
-    with open(target_file, "w") as fh:
-        fh.write(
-            template.render(get_template_overlay_context()))
-
+    try:
+        with open(target_file, "w") as fh:
+            fh.write(
+                template.render(get_template_overlay_context()))
+    except jinja2.exceptions.UndefinedError as e:
+        logging.error("Template error. You may be missing"
+                      " a mandatory environment variable : {}".format(e))
+        sys.exit(1)
     logging.info("Rendered template '{}' to file '{}'".format(template,
                                                               target_file))