diff --git a/lib/rossym/compat.h b/lib/rossym/compat.h
index 6abebb6e261..64dc549f11c 100644
--- a/lib/rossym/compat.h
+++ b/lib/rossym/compat.h
@@ -15,7 +15,7 @@ typedef int s32int;
 typedef unsigned long long u64int;
 typedef long long s64int;
 
-#ifndef WIN32
+#ifndef _WIN32
 typedef ulong size_t;
 #endif