diff --git a/gjk2d.cabal b/gjk2d.cabal
--- a/gjk2d.cabal
+++ b/gjk2d.cabal
@@ -1,5 +1,5 @@
 name:                gjk2d
-version:             0.1.0.0
+version:             0.1.0.1
 -- synopsis:
 description:         Yet another 2D GJK collision dection algorithm with Linear
 homepage:            https://github.com/suzumiyasmith/gjk2d#readme
diff --git a/src/GJK.hs b/src/GJK.hs
--- a/src/GJK.hs
+++ b/src/GJK.hs
@@ -11,8 +11,8 @@
 
 -- | Compute angle of a vector
 unAngle :: V2 Double -> Double
-unAngle (V2 ax ay) =
-  let alpha = asin $ ay / (ax * ax + ay * ay)
+unAngle a@(V2 ax ay) =
+  let alpha = asin $ ay / norm a
   in if ax < 0
        then pi - alpha
        else alpha