diff --git a/src/physics.jl b/src/physics.jl
index b9aa56f209d7e4eb9ee311eb8f6468e5d9965317..e8084b818760b943027c95a7656727810cbd1ab5 100644
--- a/src/physics.jl
+++ b/src/physics.jl
@@ -36,7 +36,7 @@ function cherenkov(track, pos::Position; dir::Union{Direction,Missing}=missing,
     Δt = t - _t
     _pos = V - (d_track * track.dir)
     _dir = normalize(_pos)
-    impact_angle = ismissing(dir) ? NaN : acos(_dir â‹… dir)
+    impact_angle = ismissing(dir) ? NaN : _dir â‹… dir
     CherenkovPhoton(
         d_closest,
         d_photon,