diff --git a/rebuild b/rebuild
index d59492b..ddab86b 100644
--- a/rebuild
+++ b/rebuild
@@ -2,4 +2,4 @@
 # when dependencies of the charm change,
 # but nothing in the charm needs to.
 # simply change the uuid to something new
-53a26c76-1178-11ec-82fd-9325926a4dcf
+acc03b90-3b6e-11ee-b46b-b7adc999a595
diff --git a/src/build.lock b/src/build.lock
index 303056d..21a2aab 100644
--- a/src/build.lock
+++ b/src/build.lock
@@ -118,6 +118,12 @@
       "vcs": null,
       "version": "21.10.1"
     },
+    {
+      "type": "python_module",
+      "package": "Cython",
+      "vcs": null,
+      "version": "0.29.36"
+    },
     {
       "type": "python_module",
       "package": "PyYAML",
@@ -243,4 +249,4 @@
       "version": "1.16.0"
     }
   ]
-}
\ No newline at end of file
+}
diff --git a/test-requirements.txt b/test-requirements.txt
index 50eef16..ec56417 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -3,6 +3,7 @@
 # choices of *requirements.txt files for OpenStack Charms:
 #     https://github.com/openstack-charmers/release-tools
 #
+#cython==0.29.36
 pyparsing<3.0.0  # aodhclient is pinned in zaza and needs pyparsing < 3.0.0, but cffi also needs it, so pin here.
 cffi==1.14.6; python_version < '3.6'  # cffi 1.15.0 drops support for py35.
 setuptools<50.0.0  # https://github.com/pypa/setuptools/commit/04e3df22df840c6bb244e9b27bc56750c44b7c85
diff --git a/tox.ini b/tox.ini
index 782b398..ff8c050 100644
--- a/tox.ini
+++ b/tox.ini
@@ -92,7 +92,8 @@ commands = stestr run --slowest {posargs}
 [testenv:pep8]
 basepython = python3
 deps = flake8==3.9.2
-       charm-tools==2.8.3
+       PyYAML==6.0.1
+       charm-tools==2.8.6
 commands = flake8 {posargs} src unit_tests
 
 [testenv:func-target]