diff --git a/include/unistd.h b/include/unistd.h
index e4e3ac59..7f2dd687 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -168,6 +168,7 @@ char *getusershell(void);
 #endif
 
 #ifdef _GNU_SOURCE
+extern char **environ;
 int setresuid(uid_t, uid_t, uid_t);
 int setresgid(gid_t, gid_t, gid_t);
 int getresuid(uid_t *, uid_t *, uid_t *);