diff --git a/xdrawchem/xdrawchem/application.cpp b/xdrawchem/xdrawchem/application.cpp
index 7e1eda7..79b0589 100644
--- a/xdrawchem/xdrawchem/application.cpp
+++ b/xdrawchem/xdrawchem/application.cpp
@@ -14,6 +14,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
+#include <unistd.h>
 
 using std::cout;
 using std::endl;