diff --git a/Project.toml b/Project.toml
index 01f36b5..19d8a11 100644
--- a/Project.toml
+++ b/Project.toml
@@ -23,6 +23,7 @@ UnPack = "3a884ed6-31ef-47d7-9d2a-63182c4928ed"
 BEASTXMLConstructor = "1"
 BeastUtils = "1"
 CSV = "0.8, 0.9, 0.10"
+Combinatorics = "1"
 DataFrames = "0.20, 0.21, 0.22, 1"
 EzXML = "1"
 JLD = "0.9, 0.10, 0.12, 0.13"