diff --git a/reactos/lib/sdk/crt/stdio/_flsbuf.c b/reactos/lib/sdk/crt/stdio/_flsbuf.c
index 07ab6716cfd..eb31137a7a5 100644
--- a/reactos/lib/sdk/crt/stdio/_flsbuf.c
+++ b/reactos/lib/sdk/crt/stdio/_flsbuf.c
@@ -78,5 +78,5 @@ _flsbuf(int ch, FILE *stream)
         return EOF;
     }
 
-    return (TCHAR)ch;
+    return ch & (sizeof(TCHAR) > sizeof(char) ? 0xffff : 0xff);
 }