diff --git a/ChatTwo/Plugin.cs b/ChatTwo/Plugin.cs
index e3c90ea..3c9e441 100755
--- a/ChatTwo/Plugin.cs
+++ b/ChatTwo/Plugin.cs
@@ -64,6 +64,15 @@ public sealed class Plugin : IDalamudPlugin
 
     internal int DeferredSaveFrames = -1;
 
+    // Serialises retention sweeps. The 24h auto-sweep on plugin load and
+    // the manual button in the Privacy tab both run on background threads;
+    // without this gate, hitting the manual button moments after a fresh
+    // plugin start would launch two sweeps in parallel and the second one
+    // would just re-do work the first one already finished. The lock guards
+    // the flag — the flag check itself bails before we touch the database.
+    internal readonly object RetentionSweepLock = new();
+    internal bool RetentionSweepRunning;
+
     internal DateTime GameStarted { get; }
 
     // Tab management needs to happen outside the chatlog window class for access reasons
@@ -405,6 +414,16 @@ public sealed class Plugin : IDalamudPlugin
 
         new Thread(() =>
         {
+            // Bail out cheaply if a manual sweep is already in flight; the
+            // lock around the actual work would queue us up otherwise and
+            // we would just re-do whatever the manual run already did.
+            lock (RetentionSweepLock)
+            {
+                if (RetentionSweepRunning)
+                    return;
+                RetentionSweepRunning = true;
+            }
+
             try
             {
                 var deleted = MessageManager.Store.DeleteByRetentionPolicy(policy, defaultDays);
@@ -429,6 +448,11 @@ public sealed class Plugin : IDalamudPlugin
             {
                 Log.Error(e, "Retention sweep failed");
             }
+            finally
+            {
+                lock (RetentionSweepLock)
+                    RetentionSweepRunning = false;
+            }
         }) { IsBackground = true }.Start();
     }
 
diff --git a/ChatTwo/Ui/SettingsTabs/Privacy.cs b/ChatTwo/Ui/SettingsTabs/Privacy.cs
index 42523af..9db5cfe 100644
--- a/ChatTwo/Ui/SettingsTabs/Privacy.cs
+++ b/ChatTwo/Ui/SettingsTabs/Privacy.cs
@@ -55,7 +55,10 @@ internal sealed class Privacy : ISettingsTab
     private long CleanupDeleteCount;
     private bool CleanupRunning;
 
-    private bool RetentionRunning;
+    // The retention-running state lives on Plugin so the auto-sweep and
+    // this manual button see the same flag. UI reads stay lock-free
+    // because ImGui is single-threaded and bool reads are atomic in .NET.
+    private bool RetentionRunning => Plugin.RetentionSweepRunning;
 
     // Export form state
     private int ExportRangeDays = 30;
@@ -410,10 +413,17 @@ internal sealed class Privacy : ISettingsTab
 
     private void StartRetentionRun()
     {
-        if (RetentionRunning)
-            return;
+        // Take the shared retention lock so we cannot fight the auto-sweep
+        // for the database connection. If the auto-sweep is already in
+        // flight we just bail — the user can press the button again once
+        // it finishes.
+        lock (Plugin.RetentionSweepLock)
+        {
+            if (Plugin.RetentionSweepRunning)
+                return;
+            Plugin.RetentionSweepRunning = true;
+        }
 
-        RetentionRunning = true;
         var policy = Plugin.Config.RetentionPerChannelDays.ToDictionary(p => (int)(ushort)p.Key, p => p.Value);
         var defaultDays = Plugin.Config.RetentionDefaultDays;
 
@@ -445,7 +455,8 @@ internal sealed class Privacy : ISettingsTab
             }
             finally
             {
-                RetentionRunning = false;
+                lock (Plugin.RetentionSweepLock)
+                    Plugin.RetentionSweepRunning = false;
             }
         }) { IsBackground = true }.Start();
     }