diff --git a/config-msvc.h b/config-msvc.h
index a39d4e7..37f1c0b 100644
--- a/config-msvc.h
+++ b/config-msvc.h
@@ -66,7 +66,7 @@
 #define HAVE_SYS_TYPES_H 1
 
 /* Define to 1 if you have the <unistd.h> header file. */
-#define HAVE_UNISTD_H 1
+#undef HAVE_UNISTD_H
 
 /* Define to 1 if `lstat' dereferences a symlink specified with a trailing
    slash. */