https://bugs.gentoo.org/420975

--- a/src/yafraycore/threadedscene.cc
+++ b/src/yafraycore/threadedscene.cc
@@ -44,6 +44,7 @@ __BEGIN_YAFRAY
 
 #include<signal.h>
 #include<sys/time.h>
+#include <unistd.h>
 
 void blockSignals(sigset_t *origmask)
 {