diff -up zstandard-0.22.0/c-ext/backend_c.c.orig zstandard-0.22.0/c-ext/backend_c.c
--- zstandard-0.22.0/c-ext/backend_c.c.orig	2023-11-01 07:04:15.000000000 +0100
+++ zstandard-0.22.0/c-ext/backend_c.c	2023-11-22 12:51:36.452480448 +0100
@@ -17,6 +17,8 @@
 
 #include <sys/sysctl.h>
 
+#elif defined(__linux__) && defined(HAVE_UNISTD_H)
+#include <unistd.h>
 #endif
 
 #include "python-zstandard.h"