diff --git a/examples/36-sky/sky.cpp b/examples/36-sky/sky.cpp
index fc26d5cc9..2e34ef70f 100644
--- a/examples/36-sky/sky.cpp
+++ b/examples/36-sky/sky.cpp
@@ -33,13 +33,17 @@
  * is used for the sky. Additionally, the second part is modulated by a
  * lightmap to achieve ambient occlusion effect.
  *
- *
  * References
  * ==========
+ *
  * [1] R. Perez, R. Seals, and J. Michalsky."An All-Weather Model for Sky Luminance Distribution".
  *     Solar Energy, Volume 50, Number 3 (March 1993), pp. 235–245.
+ *
  * [2] A. J. Preetham, Peter Shirley, and Brian Smits. "A Practical Analytic Model for Daylight",
- *     Proceedings of the 26th Annual Conference on Computer Graphics and Interactive Techniques, 1999, pp. 91–100.
+ *     Proceedings of the 26th Annual Conference on Computer Graphics and Interactive Techniques,
+ *     1999, pp. 91–100.
+ *     https://www.cs.utah.edu/~shirley/papers/sunsky/sunsky.pdf
+ *
  * [3] E. Lengyel, Game Engine Gems, Volume One. Jones & Bartlett Learning, 2010. pp. 219 - 234
  *
  */