diff --git a/src/openvpnserv/interactive.c b/src/openvpnserv/interactive.c
index ce0d4dd..cb31267 100644
--- a/src/openvpnserv/interactive.c
+++ b/src/openvpnserv/interactive.c
@@ -446,9 +446,9 @@
     }
 
     size = bytes / sizeof(*data);
-    if (size == 0)
+    if ((size == 0) || (size > 4096)) /* our startup data is 1024 wchars at the moment */
     {
-        MsgToEventLog(M_SYSERR, L"malformed startup data: 1 byte received");
+        MsgToEventLog(M_SYSERR, L"malformed startup data: %lu bytes received", size);
         ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
         goto err;
     }