diff --git a/Project.toml b/Project.toml
index 3408707..fd9cf66 100644
--- a/Project.toml
+++ b/Project.toml
@@ -30,6 +30,7 @@ FITSIO = "0.16"
 FastTransforms = "0.13, 0.14"
 Healpix = "3, 4"
 Libsharp = "0.2"
+PhysicalConstants = "0.2"
 RecipesBase = "1"
 StaticArrays = "1"
 Unitful = "1"