diff --git a/pyproject.toml b/pyproject.toml
index 31d30cc..47269d2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,6 +17,7 @@ python = "~2.7 || ^3.5"
 
 backoff = "^1.10.0"
 requests = "^2.25.1"
+"backports.functools_lru_cache" = "!=1.6.2,!=1.6.3" # https://github.com/jaraco/backports.functools_lru_cache/pull/16
 
 [tool.poetry.dev-dependencies]
 flake8 = "^3.8.4"