diff --git a/gzlib.c b/gzlib.c
index baa3e79d..7b751da4 100644
--- a/gzlib.c
+++ b/gzlib.c
@@ -4,6 +4,11 @@
  */
 
 #include "gzguts.h"
+#if defined( unix ) || defined( __unix ) || defined( __unix__ ) || \
+    (defined( __APPLE__ ) && defined( __MACH__ )) || \
+    HAVE_UNISTD_H
+#include <unistd.h>         /* lseek, read, write, close, chown, unlink, sleep, ftruncate, fsync */
+#endif
 
 #if defined(__DJGPP__)
 #  define LSEEK llseek