diff --git a/lib/libc/gen/getgrouplist.c b/lib/libc/gen/getgrouplist.c
index cb23b9b2316..9c57b703133 100644
--- a/lib/libc/gen/getgrouplist.c
+++ b/lib/libc/gen/getgrouplist.c
@@ -31,6 +31,7 @@
 
 #include <sys/types.h>
 
+#include <unistd.h>
 #include <ssp/ssp.h>
 
 extern int __getgroupmembership(const char *, gid_t, gid_t *, int, int *);