diff --git a/tox.ini b/tox.ini
index 1811c3ab3f..44fde724c1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -53,7 +53,7 @@ install_command = pip install {opts} {packages}
 # type checking on the world - just on ourselves.
 deps =
   flake8
-  mypy<0.650
+  mypy<0.740
   openapi-spec-validator
 commands =
   flake8 {posargs}
diff --git a/zuul/lib/yamlutil.py b/zuul/lib/yamlutil.py
index 2c84b06ae5..c2356da2dd 100644
--- a/zuul/lib/yamlutil.py
+++ b/zuul/lib/yamlutil.py
@@ -14,14 +14,15 @@ from yaml import YAMLObject, YAMLError  # noqa: F401
 
 try:
     # Explicit type ignore to deal with provisional import failure
+    # Details at https://github.com/python/mypy/issues/1153
     from yaml import cyaml  # type: ignore
     import _yaml
     SafeLoader = cyaml.CSafeLoader
     SafeDumper = cyaml.CSafeDumper
     Mark = _yaml.Mark
 except ImportError:
-    SafeLoader = yaml.SafeLoader
-    SafeDumper = yaml.SafeDumper
+    SafeLoader = yaml.SafeLoader  # type: ignore
+    SafeDumper = yaml.SafeDumper  # type: ignore
     Mark = yaml.Mark