diff --git a/tests/test_bad_size.yaml b/tests/test_bad_size.yaml
new file mode 100644
index 0000000..22f71cd
--- /dev/null
+++ b/tests/test_bad_size.yaml
@@ -0,0 +1,16 @@
+---
+remote: '/var/empty'
+key: 0x00000000
+
+images:
+  rootfs-minimal:
+    target: ve/docker
+    size: M10
+    kinds:
+    - tar.xz
+
+branches:
+  Sisyphus:
+    arches:
+      x86_64:
+...
diff --git a/tests/test_errors.py b/tests/test_errors.py
index 58ee2e2..703840c 100644
--- a/tests/test_errors.py
+++ b/tests/test_errors.py
@@ -119,3 +119,12 @@ class TestErrors(TestCase):
         regex = 'years.*rebuild_after'
         self.kwargs.update(config='tests/test_rebuild_after_format.yaml')
         self.assertRaisesRegex(Error, regex, CB, **self.kwargs)
+
+    def test_bad_size(self):
+        regex = 'Bad size.*'
+        cloud_build = CB(
+            config='tests/test_bad_size.yaml',
+            data_dir=self.kwargs['data_dir'],
+            no_tests=True,
+        )
+        self.assertRaisesRegex(Error, regex, cloud_build.create_images)
diff --git a/tests/test_utils.py b/tests/test_utils.py
new file mode 100644
index 0000000..7806fd5
--- /dev/null
+++ b/tests/test_utils.py
@@ -0,0 +1,28 @@
+from unittest import TestCase
+
+import shutil
+import tempfile
+
+from cloud_build import CB
+
+
+class TestUtils(TestCase):
+    def setUp(self):
+        kwargs = {
+            'data_dir': tempfile.mkdtemp(prefix='cloud_build'),
+            'config': 'tests/minimal_config.yaml',
+        }
+        self.kwargs = kwargs
+        self.cb = CB(**kwargs)
+
+    def tearDown(self):
+        shutil.rmtree(self.kwargs['data_dir'])
+
+    def test_conver_size_lower_case(self):
+        self.assertEqual(self.cb.convert_size('200k'), '204800')
+
+    def test_conver_size_upper_case(self):
+        self.assertEqual(self.cb.convert_size('1M'), '1048576')
+
+    def test_conver_size_real(self):
+        self.assertEqual(self.cb.convert_size('0.1G'), '107374182')