diff --git a/HandmadeMath.h b/HandmadeMath.h
index 4bdca83..8877e6f 100644
--- a/HandmadeMath.h
+++ b/HandmadeMath.h
@@ -352,6 +352,7 @@ HMM_LengthSquareRoot(hmm_vec3 A)
     return (Result);
 }
 
+// Refer to https://en.wikipedia.org/wiki/Fast_inverse_square_root
 HINLINE float
 HMM_FastInverseSquareRoot(float Number)
 {