diff --git a/lib/http_ntlm.c b/lib/http_ntlm.c
index 8205a8fea1..4bbd0dda7f 100644
--- a/lib/http_ntlm.c
+++ b/lib/http_ntlm.c
@@ -44,6 +44,10 @@
 #include <stdlib.h>
 #include <ctype.h>
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 #include "urldata.h"
 #include "sendf.h"
 #include "strequal.h"