diff --git a/Sources/Rotation.swift b/Sources/Rotation.swift
index e5a9f605..071245d3 100644
--- a/Sources/Rotation.swift
+++ b/Sources/Rotation.swift
@@ -225,7 +225,7 @@ extension Rotation {
     }
 
     init(unchecked axis: Vector, angle: Angle) {
-        assert(axis.isNormalized)
+        assert(axis.isNormalized, "Axis length is \(axis.length)")
         let r = -angle / 2
         let a = axis * sin(r)
         self.init(unchecked: a.x, a.y, a.z, cos(r))