diff --git a/pyproject.toml b/pyproject.toml
index c1de1bf..b003c82 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,6 +26,7 @@ kubernetes = "^21.7.0"
 requests = "^2.24.0"
 requests-toolbelt = "^0.9.1"
 click = "^7.1.2"
+cython = "<3.0.0"
 
 # Docs build dependencies
 sphinx = { version = "^3.3.0", optional = true }