diff --git a/win/rfb_win32/SInput.cxx b/win/rfb_win32/SInput.cxx
index f634566..111a4d9 100644
--- a/win/rfb_win32/SInput.cxx
+++ b/win/rfb_win32/SInput.cxx
@@ -66,7 +66,7 @@
 };
 
 static DWORD buttonDataMapping[8] = {
-  0, 0, 0, 120, -120, 0, 0, 0
+  0, 0, 0, 120, (DWORD)-120, 0, 0, 0
 };
 
 win32::SPointer::SPointer()