diff --git a/requirements.txt b/requirements.txt
index cf7e0dfef53e7731aeac46400a6c907ce2ec0658..3e1e9b0cc22d92a2c684c633837efa32dc6a2df4 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,3 +10,4 @@ uproot4
 awkward1>=0.4.4
 pandas
 mendeleev
+proposal