diff --git a/vm/nga-c/retro.c b/vm/nga-c/retro.c
index db86aa1..8c42ceb 100644
--- a/vm/nga-c/retro.c
+++ b/vm/nga-c/retro.c
@@ -22,6 +22,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <time.h>
+#include <unistd.h>
 
 #ifdef ENABLE_SIGNALS
 #include <signal.h>