diff --git a/Source/cmQtAutomoc.cxx b/Source/cmQtAutomoc.cxx
index 8b899bc628..ca27530fb2 100644
--- a/Source/cmQtAutomoc.cxx
+++ b/Source/cmQtAutomoc.cxx
@@ -20,6 +20,9 @@
 #include <cmsys/Terminal.h>
 
 #include <string.h>
+#if defined(__APPLE__)
+#include <unistd.h>
+#endif
 
 #include "cmQtAutomoc.h"