diff --git a/dlls/msctf/tests/inputprocessor.c b/dlls/msctf/tests/inputprocessor.c
index f4f737f..c445b41 100644
--- a/dlls/msctf/tests/inputprocessor.c
+++ b/dlls/msctf/tests/inputprocessor.c
@@ -1850,8 +1850,8 @@
         {
             WCHAR str[50];
             CHAR strA[50];
-            StringFromGUID2(&g,str,50);
-            WideCharToMultiByte(CP_ACP,0,str,50,strA,50,0,0);
+            StringFromGUID2(&g,str,sizeof(str)/sizeof(str[0]));
+            WideCharToMultiByte(CP_ACP,0,str,-1,strA,sizeof(strA),0,0);
             trace("found %s\n",strA);
             if (present && IsEqualGUID(present,&g))
                 found = TRUE;