diff --git a/Project.toml b/Project.toml
index cee72a7..ee4848b 100644
--- a/Project.toml
+++ b/Project.toml
@@ -12,6 +12,7 @@ Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"
 UnitfulAstro = "6112ee07-acf9-5e0f-b108-d242c714bf9f"
 
 [compat]
+PhysicalConstants = "0.2"
 Roots = "2"
 Unitful = "1"
 QuadGK = "2"