diff --git a/src/physfs_lzmasdk.h b/src/physfs_lzmasdk.h
index 3a79b5b..593fb10 100644
--- a/src/physfs_lzmasdk.h
+++ b/src/physfs_lzmasdk.h
@@ -83,7 +83,7 @@ typedef unsigned long UInt64;
 
 #else
 
-#if defined(_MSC_VER) || defined(__BORLANDC__)
+#if defined(_MSC_VER) || defined(__BORLANDC__) || defined(__WATCOMC__)
 typedef __int64 Int64;
 typedef unsigned __int64 UInt64;
 #define UINT64_CONST(n) n