diff --git a/package-lock.json b/package-lock.json
index f0c51fa..4e45214 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "folio",
-  "version": "0.1.14",
+  "version": "0.1.15",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "folio",
-      "version": "0.1.14",
+      "version": "0.1.15",
       "license": "MIT",
       "dependencies": {
         "@tiptap/core": "^2.27.2",
diff --git a/package.json b/package.json
index 099acf8..85cbb3f 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "folio",
-  "version": "0.1.14",
+  "version": "0.1.15",
   "description": "A simple, local, open-source desktop writing app.",
   "productName": "Folio",
   "author": "Folio Contributors",
diff --git a/src/main/index.ts b/src/main/index.ts
index e666950..3596ddb 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -1423,4 +1423,8 @@ if (app.requestSingleInstanceLock()) {
     }
     if (f) openFromArg(f);
   });
+} else {
+  // Lost the lock: another Folio is already running. Without this quit the
+  // second process falls through to whenReady() and opens a duplicate window.
+  app.quit();
 }