diff --git a/lib/http_proxy.c b/lib/http_proxy.c
index 99f3f0a70979babd2cb0de84c481c90a96dc969a..89cfb72c8354cb1d1c26fba9db958aec80ace9a7 100644
--- a/lib/http_proxy.c
+++ b/lib/http_proxy.c
@@ -24,6 +24,9 @@
 
 #if !defined(CURL_DISABLE_PROXY) && !defined(CURL_DISABLE_HTTP)
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
 #include "urldata.h"
 #include <curl/curl.h>
 #include "http_proxy.h"