diff --git a/setup.py b/setup.py
index ff2352258..8dabb5684 100755
--- a/setup.py
+++ b/setup.py
@@ -304,7 +304,9 @@ def initialize_options(self) -> None:
           # what we support
           #
           # https://github.com/aws/aws-cli/blob/develop/setup.py
-          'PyYAML>=3.10,<5.5',
+          # #### NEW UNFORTUNATE CONSTRAINTS #####
+          # https://github.com/yaml/pyyaml/issues/724
+          'PyYAML>=3.10,<=5.3.1',
           # Not sure how/if interface will change in db-facts, so
           # let's be conservative about what we're specifying for now.
           'db-facts>=4,<5',