diff --git a/emper/Runtime.hpp b/emper/Runtime.hpp
index 414befab7e26b9e9dac1314c1ee774416f3eb20b..69b6ff3b2b90a66607189e5b2c3f6b1d1181d759 100644
--- a/emper/Runtime.hpp
+++ b/emper/Runtime.hpp
@@ -84,6 +84,7 @@ public:
 
 	Fiber* nextFiber();
 
+	// https://stackoverflow.com/a/3747462/194894
 	static inline int rand() {
 		seed = 214013 * seed + 2531011;
 		return (seed >> 16) & 0x7FFF;