diff --git a/common/zlib/gzguts.h b/common/zlib/gzguts.h
index eba7208..23229ca 100644
--- a/common/zlib/gzguts.h
+++ b/common/zlib/gzguts.h
@@ -3,6 +3,11 @@
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
+// UEFITool: required for macOS
+#ifndef _WIN32
+  #include <unistd.h>
+#endif
+
 #ifdef _LARGEFILE64_SOURCE
 #  ifndef _LARGEFILE_SOURCE
 #    define _LARGEFILE_SOURCE 1