diff --git a/libc/isystem/unistd.h b/libc/isystem/unistd.h
index fb2935447..efa39c87c 100644
--- a/libc/isystem/unistd.h
+++ b/libc/isystem/unistd.h
@@ -2,6 +2,7 @@
 #define LIBC_ISYSTEM_UNISTD_H_
 #include "libc/calls/calls.h"
 #include "libc/calls/weirdtypes.h"
+#include "libc/runtime/sysconf.h"
 #include "libc/sysv/consts/fileno.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/ok.h"