diff --git a/dep/zlib/src/gzguts.h b/dep/zlib/src/gzguts.h
index 990a4d251..1b56c48a5 100644
--- a/dep/zlib/src/gzguts.h
+++ b/dep/zlib/src/gzguts.h
@@ -37,6 +37,8 @@
 
 #if defined(__TURBOC__) || defined(_MSC_VER) || defined(_WIN32)
 #  include <io.h>
+#else
+#  include <unistd.h>
 #endif
 
 #if defined(_WIN32) || defined(__CYGWIN__)