diff --git a/src/os_mswin.c b/src/os_mswin.c
index 6b7e896..6ee6379 100644
--- a/src/os_mswin.c
+++ b/src/os_mswin.c
@@ -2548,7 +2548,7 @@
     data.cbData = (DWORD)STRLEN(p_enc) + 1;
     data.lpData = p_enc;
 #else
-    data.cbData = STRLEN("latin1") + 1;
+    data.cbData = (DWORD)STRLEN("latin1") + 1;
     data.lpData = "latin1";
 #endif
     (void)SendMessage(target, WM_COPYDATA, (WPARAM)message_window,