diff --git a/HellionChat/Themes/ThemeJsonLoader.cs b/HellionChat/Themes/ThemeJsonLoader.cs
index e340165..79b69dc 100644
--- a/HellionChat/Themes/ThemeJsonLoader.cs
+++ b/HellionChat/Themes/ThemeJsonLoader.cs
@@ -63,7 +63,11 @@ internal static class ThemeJsonLoader
 
     public static Theme LoadFromFile(string path)
     {
-        var json = File.ReadAllText(path);
+        // FileShare.Read lets concurrent readers and well-behaved editors share
+        // the handle; atomic-replace editors still raise IOException, caught upstream.
+        using var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
+        using var reader = new StreamReader(stream);
+        var json = reader.ReadToEnd();
         return LoadFromString(json);
     }
 
diff --git a/HellionChat/Themes/ThemeRegistry.cs b/HellionChat/Themes/ThemeRegistry.cs
index 5b3ce23..82ea605 100644
--- a/HellionChat/Themes/ThemeRegistry.cs
+++ b/HellionChat/Themes/ThemeRegistry.cs
@@ -52,6 +52,16 @@ public sealed class ThemeRegistry
 
     public void Switch(string slug) => _active = Get(slug);
 
+    // 0x80070020 = SHARING_VIOLATION, 0x80070021 = LOCK_VIOLATION. Other
+    // IO failures are permanent and get the theme dropped instead of retried.
+    internal static bool IsRecoverableFileLock(Exception? ex)
+    {
+        if (ex is not IOException io)
+            return false;
+        var code = (uint)io.HResult;
+        return code == 0x80070020u || code == 0x80070021u;
+    }
+
     // Custom-Themes werden lazy aus dem Verzeichnis geladen, Cache mit
     // LastWriteTime-Token. Eine geänderte JSON wird beim nächsten Lookup
     // neu eingelesen.
@@ -89,12 +99,16 @@ public sealed class ThemeRegistry
                     theme.RecomputeAbgrCache();
                     _customCache[key] = (theme, stamp);
                 }
-                catch (Exception ex)
+                catch (Exception ex) when (IsRecoverableFileLock(ex))
+                {
+                    // Editor mid-save: keep the cached snapshot, leave the stamp
+                    // alone so the next refresh retries automatically.
+                    Plugin.Log.Debug($"Custom theme {Path.GetFileName(path)} is locked, keeping last known good");
+                    if (cached.Theme is not null)
+                        theme = cached.Theme;
+                }
+                catch (Exception)
                 {
-                    // Logging passiert in Plugin.cs durch den Aufrufer; hier still
-                    // ignorieren, damit ein einzelnes kaputtes JSON nicht alle
-                    // Custom-Themes blockt.
-                    _ = ex;
                     continue;
                 }
             }