diff --git a/config/requirements.txt b/config/requirements.txt
index a95b653..20c86b9 100644
--- a/config/requirements.txt
+++ b/config/requirements.txt
@@ -60,3 +60,5 @@ uproot
 backports.lzma
 lz4
 xxhash
+# setuptools_scm comes via tornado. newer versions of setuptools_scm do not support py2
+setuptools_scm<6.0