diff --git a/dlls/msi/suminfo.c b/dlls/msi/suminfo.c
index d3db44aa36e..df35c4d0d4c 100644
--- a/dlls/msi/suminfo.c
+++ b/dlls/msi/suminfo.c
@@ -607,9 +607,8 @@ static UINT get_prop( MSIHANDLE handle, UINT uiProperty, UINT *puiDataType,
 
             if( str->unicode )
             {
-                len = MultiByteToWideChar( CP_ACP, 0, prop->u.pszVal, -1,
-                                           str->str.w, *pcchValueBuf );
-                len--;
+                len = MultiByteToWideChar( CP_ACP, 0, prop->u.pszVal, -1, NULL, 0 ) - 1;
+                MultiByteToWideChar( CP_ACP, 0, prop->u.pszVal, -1, str->str.w, *pcchValueBuf );
             }
             else
             {