diff --git a/fluid/undo.cxx b/fluid/undo.cxx
index c0590f78e..77a2f2f31 100644
--- a/fluid/undo.cxx
+++ b/fluid/undo.cxx
@@ -33,7 +33,7 @@
 #if defined(WIN32) && !defined(__CYGWIN__)
 #  include <io.h>
 #  include <windows.h>
-#  define getpid GetCurrentProcessId
+#  define getpid (int)GetCurrentProcessId
 #else
 #  include <unistd.h>
 #endif // WIN32 && !__CYGWIN__