diff --git a/.env.example b/.env.example
index b26a250..aeaa94a 100644
--- a/.env.example
+++ b/.env.example
@@ -10,7 +10,7 @@
 PROJECT_NAME=jama
 
 # Image version to run (set by build.sh, or use 'latest')
-JAMA_VERSION=0.9.30
+JAMA_VERSION=0.9.31
 
 # App port — the host port Docker maps to the container
 PORT=3000
diff --git a/backend/package.json b/backend/package.json
index b6a5c8f..8e3fe6b 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -1,6 +1,6 @@
 {
   "name": "jama-backend",
-  "version": "0.9.30",
+  "version": "0.9.31",
   "description": "TeamChat backend server",
   "main": "src/index.js",
   "scripts": {
diff --git a/backend/src/routes/usergroups.js b/backend/src/routes/usergroups.js
index c0c5eef..4655c71 100644
--- a/backend/src/routes/usergroups.js
+++ b/backend/src/routes/usergroups.js
@@ -69,6 +69,15 @@ router.post('/multigroup', authMiddleware, adminMiddleware, (req, res) => {
   if (db.prepare('SELECT id FROM multi_group_dms WHERE LOWER(name) = LOWER(?)').get(name.trim())) {
     return res.status(400).json({ error: 'Name already in use' });
   }
+  // Check for duplicate user group set
+  const newGroupIds = [...new Set(userGroupIds.map(Number).filter(Boolean))].sort();
+  const allDms = db.prepare('SELECT id, name FROM multi_group_dms').all();
+  for (const existing of allDms) {
+    const existingIds = db.prepare('SELECT user_group_id FROM multi_group_dm_members WHERE multi_group_dm_id = ?').all(existing.id).map(r => r.user_group_id).sort();
+    if (existingIds.length === newGroupIds.length && existingIds.every((id, i) => id === newGroupIds[i])) {
+      return res.status(400).json({ error: `DM not created — "${existing.name}" already exists with the same member groups.` });
+    }
+  }
   const admin = db.prepare('SELECT id FROM users WHERE is_default_admin = 1').get();
   const dmResult = db.prepare(`INSERT INTO groups (name, type, owner_id, is_managed) VALUES (?, 'private', ?, 1)`).run(name.trim(), admin?.id || req.user.id);
   const dmGroupId = dmResult.lastInsertRowid;
@@ -179,6 +188,17 @@ router.post('/', authMiddleware, adminMiddleware, (req, res) => {
   if (db.prepare('SELECT id FROM user_groups WHERE LOWER(name) = LOWER(?)').get(name.trim())) {
     return res.status(400).json({ error: 'A group with that name already exists' });
   }
+  // Check for duplicate member set
+  const newIds = [...new Set((Array.isArray(memberIds) ? memberIds : []).map(Number).filter(Boolean))].sort();
+  if (newIds.length > 0) {
+    const allGroups = db.prepare('SELECT id, name FROM user_groups').all();
+    for (const existing of allGroups) {
+      const existingIds = db.prepare('SELECT user_id FROM user_group_members WHERE user_group_id = ?').all(existing.id).map(r => r.user_id).sort();
+      if (existingIds.length === newIds.length && existingIds.every((id, i) => id === newIds[i])) {
+        return res.status(400).json({ error: `Group not created — "${existing.name}" already exists with the same members.` });
+      }
+    }
+  }
   const admin = db.prepare('SELECT id FROM users WHERE is_default_admin = 1').get();
   const dmResult = db.prepare(`INSERT INTO groups (name, type, owner_id, is_readonly, is_direct, is_managed) VALUES (?, 'private', ?, 0, 0, 1)`).run(name.trim(), admin?.id || req.user.id);
   const dmGroupId = dmResult.lastInsertRowid;
diff --git a/build.sh b/build.sh
index 07e8c61..4c6ac88 100644
--- a/build.sh
+++ b/build.sh
@@ -13,7 +13,7 @@
 # ─────────────────────────────────────────────────────────────
 set -euo pipefail
 
-VERSION="${1:-0.9.30}"
+VERSION="${1:-0.9.31}"
 ACTION="${2:-}"
 REGISTRY="${REGISTRY:-}"
 IMAGE_NAME="jama"
diff --git a/frontend/package.json b/frontend/package.json
index 1c25a8a..0d98fcc 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -1,6 +1,6 @@
 {
   "name": "jama-frontend",
-  "version": "0.9.30",
+  "version": "0.9.31",
   "private": true,
   "scripts": {
     "dev": "vite",