diff --git a/Project.toml b/Project.toml
index a1efa44..3ada5ba 100644
--- a/Project.toml
+++ b/Project.toml
@@ -21,6 +21,7 @@ AssigningSecondaryStructure = "0.4"
 Backboner = "0.11"
 BioStructures = "4"
 OrderedCollections = "1"
+PeriodicTable = "1"
 Zygote = "0.6"
 julia = "1"