diff --git a/system/pci.c b/system/pci.c
index 812aa16..62ff428 100644
--- a/system/pci.c
+++ b/system/pci.c
@@ -22,6 +22,7 @@
 #include "io.h"
 
 #include "pci.h"
+#include "unistd.h"
 
 //------------------------------------------------------------------------------
 // Constants