diff --git a/expat/xmlwf/xmlwf.c b/expat/xmlwf/xmlwf.c
index 3b574dc7..1eb78d4e 100755
--- a/expat/xmlwf/xmlwf.c
+++ b/expat/xmlwf/xmlwf.c
@@ -31,6 +31,10 @@ Contributor(s):
 #include <io.h>
 #endif
 
+#ifdef _POSIX_SOURCE
+#include <unistd.h>
+#endif
+
 #ifndef O_BINARY
 #ifdef _O_BINARY
 #define O_BINARY _O_BINARY