diff --git a/setup.py b/setup.py
index 2fbbd04..8bd31bd 100644
--- a/setup.py
+++ b/setup.py
@@ -43,6 +43,7 @@
 
 VECTORS_DEPENDENCY = "cryptography_vectors=={0}".format(about['__version__'])
 
+# `setup_requirements` must be kept in sync with `pyproject.toml`
 setup_requirements = ["cffi>=1.7,!=1.11.3"]
 
 if platform.python_implementation() == "PyPy":