diff --git a/test/registry_tests.py b/test/registry_tests.py
index 1a320f40d..075b761fc 100644
--- a/test/registry_tests.py
+++ b/test/registry_tests.py
@@ -38,7 +38,7 @@ from endpoints.csrf import generate_csrf_token
 from endpoints.v1 import v1_bp
 from endpoints.v2 import v2_bp
 from endpoints.verbs import verbs
-from image.docker.schema1 import DockerSchema1ManifestBuilder, DockerSchema1Manifest
+from image.docker.schema1 import DockerSchema1ManifestBuilder
 from initdb import wipe_database, initialize_database, populate_database
 from jsonschema import validate as validate_schema
 from util.security.registry_jwt import decode_bearer_header
@@ -1927,6 +1927,9 @@ class ACIConversionTests(RegistryTestCaseMixin, V1RegistryPushMixin, LiveServerT
     # new generation of the image.
     self.conduct('POST', '/__test/clearderivedcache')
 
+    # Ensures the generated signature will be different.
+    time.sleep(1)
+
     _, converted_again = self.get_converted_image()
     second_hash = hashlib.sha256(converted_again).hexdigest()
     self.assertEquals(second_hash, first_hash)