diff --git a/app.py b/app.py
index 5f1afcd..7683ef0 100644
--- a/app.py
+++ b/app.py
@@ -216,13 +216,12 @@ def get_vm_live_stats():
             balloon_unused = s.get("balloon_unused", 0)
             balloon_rss = s.get("balloon_rss", 0)
 
-            if balloon_avail > 0:
+            if balloon_avail > 0 and balloon_unused >= 0:
                 mem_total = balloon_avail // 1024  # KiB to MB
                 mem_used = (balloon_avail - balloon_unused) // 1024
-            elif balloon_rss > 0:
-                mem_total = 0
-                mem_used = balloon_rss // 1024
             else:
+                # No guest-side stats (e.g. Windows without full guest agent).
+                # Mark as unavailable — frontend will show allocated RAM only.
                 mem_total = 0
                 mem_used = 0