diff --git a/CHANGELOG.md b/CHANGELOG.md
index c2c5d80..6f15712 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,12 @@
 All notable changes to this project are documented here, following
 [Keep a Changelog](https://keepachangelog.com/) and semantic versioning.
 
+## [0.1.13] - 2026-09-16
+
+### Fixed
+
+- Repair orphan managed-block end markers instead of duplicating them.
+
 ## [0.1.12] - 2026-09-16
 
 ### Fixed
diff --git a/package-lock.json b/package-lock.json
index 71e5608..fc7b59a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "ctxtrim",
-  "version": "0.1.12",
+  "version": "0.1.13",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "ctxtrim",
-      "version": "0.1.12",
+      "version": "0.1.13",
       "license": "MIT",
       "bin": {
         "ctxtrim": "bin/ctxtrim.js"
diff --git a/package.json b/package.json
index 95b3207..d1e1015 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "ctxtrim",
-  "version": "0.1.12",
+  "version": "0.1.13",
   "description": "Trim what bloats your AI coding context. Scan a repo, find the high-cost/low-value files ballooning your Claude Code / Cursor / Codex context, and write ignore files to cut token cost. Zero dependencies.",
   "type": "module",
   "bin": {
diff --git a/src/ignore.js b/src/ignore.js
index 5d3b89a..9d19e8c 100644
--- a/src/ignore.js
+++ b/src/ignore.js
@@ -22,7 +22,7 @@ export function block(patterns) {
 export function merge(existing, patterns) {
   const b = block(patterns);
   const startIndex = existing.indexOf(START);
-  const endIndex = existing.indexOf(END, startIndex + START.length);
+  const endIndex = existing.indexOf(END, startIndex === -1 ? 0 : startIndex + START.length);
   if (startIndex !== -1 && endIndex !== -1) {
     return existing.replace(new RegExp(escape(START) + "[\\s\\S]*?" + escape(END)), b).trimEnd() + "\n";
   }
@@ -30,6 +30,10 @@ export function merge(existing, patterns) {
     const base = existing.slice(0, startIndex).trim();
     return (base ? base + "\n\n" : "") + b + "\n";
   }
+  if (endIndex !== -1) {
+    const base = (existing.slice(0, endIndex) + existing.slice(endIndex + END.length)).trim();
+    return (base ? base + "\n\n" : "") + b + "\n";
+  }
   const base = existing.trim();
   return (base ? base + "\n\n" : "") + b + "\n";
 }
diff --git a/test/ctxtrim.test.js b/test/ctxtrim.test.js
index 0ccd82c..88e3864 100644
--- a/test/ctxtrim.test.js
+++ b/test/ctxtrim.test.js
@@ -158,6 +158,14 @@ test("ignore merge repairs a managed block with no end marker", () => {
   assert.equal((repaired.match(/ctxtrim \(managed\)/g) || []).length, 2);
 });
 
+test("ignore merge repairs an orphan end marker", () => {
+  const existing = "# my own rule\n# <<< ctxtrim (managed) <<<\n";
+  const repaired = merge(existing, ["dist/"]);
+  assert.equal((repaired.match(/ctxtrim \(managed\)/g) || []).length, 2);
+  assert.ok(repaired.includes("# my own rule"));
+  assert.ok(repaired.includes(block(["dist/"])));
+});
+
 test("clean repo (only source) reports nothing to trim", () => {
   // scanning the src subdir alone = only source
   const s = scanRepo(join(repo, "src"));