diff --git a/Source/LibTIFF/tif_config.h b/Source/LibTIFF/tif_config.h
index c227a9d..08fa344 100644
--- a/Source/LibTIFF/tif_config.h
+++ b/Source/LibTIFF/tif_config.h
@@ -189,7 +189,10 @@
 #define HAVE_SYS_TYPES_H 1
 
 /* Define to 1 if you have the <unistd.h> header file. */
+#ifndef WIN32
+// On Windows, this conflicts with zlib's configuration.
 #define HAVE_UNISTD_H 1
+#endif
 
 /* Define to 1 if you have the <windows.h> header file. */
 /* #undef HAVE_WINDOWS_H */