diff --git a/src/xrt/drivers/ohmd/oh_device.c b/src/xrt/drivers/ohmd/oh_device.c
index 8f1e8a6fec4e5a1c4437896e20bd2a663ee83a66..7fdef5b2bcb65aaf938b1270bd3575742468336b 100644
--- a/src/xrt/drivers/ohmd/oh_device.c
+++ b/src/xrt/drivers/ohmd/oh_device.c
@@ -10,6 +10,7 @@
 
 #include <math.h>
 #include <stdio.h>
+#include <unistd.h>
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>