diff --git a/requirements.txt b/requirements.txt
index 1e71e83e77d7521cde36bf64086741dcb1a20084..90b38c43f12a09986959d403ae20cc8ac4b1335a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,3 @@
+docopt
 uproot>=3.10.12
 setuptools_scm