diff --git a/src/mynonlinearity.cc b/src/mynonlinearity.cc
index 1a09904e61cd4ab9759b42c7ecbe0b2a2e9af2b6..0b6489bafaddf2c0d33b69c7f079b1a7e0b92c7b 100644
--- a/src/mynonlinearity.cc
+++ b/src/mynonlinearity.cc
@@ -32,10 +32,9 @@ class MyNonlinearity {
       return;
     }
     double const un = u.two_norm();
-    double const ndotp = (u * v) / (un * v.two_norm());
+    double const ndotp = (u * v) / un;
+    // Our coordinate system is now such that v is a unit vector!
     if (ndotp > 0) {
-      // If we had |v| = 1, this would be
-      // <f'_pm(|u|)*u/|u|,v>
       D[1] = ndotp * func_.rightDifferential(un);
       D[0] = ndotp * func_.leftDifferential(un);
     } else {