diff --git a/gzguts.h b/gzguts.h
index 13e81791ef3f2309aeaae778e4ad4cc158bdca9e..ee3f281aa5713659c007fed390009490afb60c15 100644
--- a/gzguts.h
+++ b/gzguts.h
@@ -27,6 +27,10 @@
 #endif
 #include <fcntl.h>
 
+#ifdef _WIN32
+#  include <stddef.h>
+#endif
+
 #if defined(__TURBOC__) || defined(_MSC_VER) || defined(_WIN32)
 #  include <io.h>
 #endif
diff --git a/gzlib.c b/gzlib.c
index e90b6adb089bfb472cd195bbbe55d93eb765ca63..b99c26c7b53ea63a566ea1ac4fc361dfed45d259 100644
--- a/gzlib.c
+++ b/gzlib.c
@@ -275,7 +275,7 @@ gzFile ZEXPORT gzdopen(fd, mode)
 /* -- see zlib.h -- */
 #ifdef _WIN32
 gzFile ZEXPORT gzopen_w(path, mode)
-    const w_char *path;
+    const wchar_t *path;
     const char *mode;
 {
     return gz_open(path, -2, mode);
diff --git a/zlib.h b/zlib.h
index 361d72f5d83692b105ce550364d1640167be7920..901339c57e0be4fd1a2793325ef4b839775c5906 100644
--- a/zlib.h
+++ b/zlib.h
@@ -1733,7 +1733,7 @@ ZEXTERN int            ZEXPORT inflateUndermine OF((z_streamp, int));
 ZEXTERN int            ZEXPORT inflateResetKeep OF((z_streamp));
 ZEXTERN int            ZEXPORT deflateResetKeep OF((z_streamp));
 #if defined(_WIN32) && !defined(Z_SOLO)
-ZEXTERN gzFile         ZEXPORT gzopen_w OF((const w_char *path,
+ZEXTERN gzFile         ZEXPORT gzopen_w OF((const wchar_t *path,
                                             const char *mode));
 #endif