diff --git a/Source/CTest/Curl/multi.c b/Source/CTest/Curl/multi.c
index 5ccd337f1e..630342b8e8 100644
--- a/Source/CTest/Curl/multi.c
+++ b/Source/CTest/Curl/multi.c
@@ -30,6 +30,9 @@
 #include "transfer.h"
 #include "url.h"
 #include "connect.h"
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
 
 /* The last #include file should be: */
 #ifdef MALLOCDEBUG