diff --git a/mempalace/layers.py b/mempalace/layers.py
index b20c656..d549afe 100644
--- a/mempalace/layers.py
+++ b/mempalace/layers.py
@@ -287,7 +287,7 @@ class Layer3:
         for i, (doc, meta, dist) in enumerate(zip(docs, metas, dists), 1):
             meta = meta or {}
             doc = doc or ""
-            similarity = round(1 - dist, 3)
+            similarity = round(max(0.0, 1 - dist), 3)
             wing_name = meta.get("wing", "?")
             room_name = meta.get("room", "?")
             source = Path(meta.get("source_file", "")).name if meta.get("source_file") else ""
diff --git a/mempalace/mcp_server.py b/mempalace/mcp_server.py
index 715023d..46982bb 100644
--- a/mempalace/mcp_server.py
+++ b/mempalace/mcp_server.py
@@ -740,7 +740,7 @@ def tool_check_duplicate(content: str, threshold: float = 0.9):
         if results["ids"] and results["ids"][0]:
             for i, drawer_id in enumerate(results["ids"][0]):
                 dist = results["distances"][0][i]
-                similarity = round(1 - dist, 3)
+                similarity = round(max(0.0, 1 - dist), 3)
                 if similarity >= threshold:
                     # Chroma 1.5.x can return None for partially-flushed rows;
                     # coerce to empty sentinels so downstream .get() is safe.