diff --git a/Project.toml b/Project.toml
index ca188d4..b97031c 100644
--- a/Project.toml
+++ b/Project.toml
@@ -24,6 +24,7 @@ VegaDatasets = "0ae4a718-28b7-58ec-9efb-cded64d6d5b4"
 VegaLite = "112f6efa-9a02-5b7d-90c0-432ed331239a"
 
 [compat]
+SpecialFunctions = "2"
 julia = "1.1"
 
 [extras]