diff --git a/include/bsd/unistd.h b/include/bsd/unistd.h
index 167241b..20b0993 100644
--- a/include/bsd/unistd.h
+++ b/include/bsd/unistd.h
@@ -59,7 +59,11 @@ int bsd_getopt(int argc, char * const argv[], const char *shortopts);
 mode_t getmode(const void *set, mode_t mode);
 void *setmode(const char *mode_str);
 
+#if !defined(__GLIBC__) || \
+    !__GLIBC_PREREQ(2, 34) || \
+    !defined(_DEFAULT_SOURCE)
 void closefrom(int lowfd);
+#endif
 
 /* Compatibility with sendmail implementations. */
 #define initsetproctitle(c, a, e) setproctitle_init((c), (a), (e))