diff --git a/CREDITS b/CREDITS
index 810f0b4..66604eb 100644
--- a/CREDITS
+++ b/CREDITS
@@ -43,3 +43,6 @@ https://github.com/erich666/GraphicsGems/blob/master/gems/TransBox.c
 6. Cull frustum
 http://www.txutxi.com/?p=584
 http://old.cescg.org/CESCG-2002/DSykoraJJelinek/
+
+7. Quaternions
+Initial mat4_quat is borrowed from Apple's simd library