diff --git a/requirements-dev.txt b/requirements-dev.txt
index b4c511930d..62f7e9e836 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -6,7 +6,7 @@ stubserver>=1.1,<2
 setuptools>=51.3.3,<63
 sphinx>=4,<6
 cwltest>=2.2.20211116163652
-mypy==0.982
+mypy==0.991
 types-requests
 types-setuptools
 types-boto
diff --git a/src/toil/cwl/utils.py b/src/toil/cwl/utils.py
index 5beb7d8564..37ad82576a 100644
--- a/src/toil/cwl/utils.py
+++ b/src/toil/cwl/utils.py
@@ -137,11 +137,7 @@ def visit_cwl_class_and_reduce(
     return results
 
 
-# Define a recursive type to represent a directory structure.
-# The only problem is that MyPy can't yet type check recursive types like this.
-# See: https://github.com/python/mypy/issues/731
-# So we have to tell MyPy to ignore it.
-DirectoryStructure = Dict[str, Union[str, "DirectoryStructure"]]  # type: ignore
+DirectoryStructure = Dict[str, Union[str, "DirectoryStructure"]]
 
 
 def download_structure(