diff --git a/lib/spack/docs/requirements.txt b/lib/spack/docs/requirements.txt
index 416eb7edaf4..648f3c40b5d 100644
--- a/lib/spack/docs/requirements.txt
+++ b/lib/spack/docs/requirements.txt
@@ -10,3 +10,4 @@ python-levenshtein
 # https://stackoverflow.com/questions/67542699
 docutils <0.17
 pygments <2.13
+urllib3 <2