diff --git a/Source/cmNinjaNormalTargetGenerator.cxx b/Source/cmNinjaNormalTargetGenerator.cxx
index 3e5ac4175a..be7739e1ac 100644
--- a/Source/cmNinjaNormalTargetGenerator.cxx
+++ b/Source/cmNinjaNormalTargetGenerator.cxx
@@ -20,6 +20,11 @@
 #include <assert.h>
 #include <algorithm>
 
+#ifndef _WIN32
+#include <unistd.h>
+#endif
+
+
 cmNinjaNormalTargetGenerator::
 cmNinjaNormalTargetGenerator(cmTarget* target)
   : cmNinjaTargetGenerator(target)