diff --git a/src/registry.js b/src/registry.js
index 2341b23..e06788a 100644
--- a/src/registry.js
+++ b/src/registry.js
@@ -10,7 +10,9 @@ const USER_ID = process.env.SOLEM_USER_ID || '5de53bca7ed4c45c2cfe067f';
 const registry = new Map();
 
 function makeSlug(type, serial) {
-  const suffix = (serial || '').slice(-6).toLowerCase();
+  // Serial format: PPPPPP SSSSSS 0001 — device identifier is at positions 6-11
+  const s = serial || '';
+  const suffix = (s.length >= 12 ? s.slice(6, 12) : s.slice(-6)).toLowerCase();
   return `${type}_${suffix}`.replace(/[^a-z0-9_]/g, '_');
 }