diff --git a/lib/shared/settings.js b/lib/shared/settings.js
index f0932107..8ece9c51 100644
--- a/lib/shared/settings.js
+++ b/lib/shared/settings.js
@@ -110,6 +110,8 @@ export class ConfigManager extends GObject.Object {
           const defaultContents = this.loadFileContents(defaultFile);
           Logger.trace(defaultContents);
           createdStream.write_all(defaultContents, null);
+          // close it, or the file can stay empty (#415)
+          createdStream.close(null);
         }
       }
     }
@@ -137,7 +139,29 @@ export class ConfigManager extends GObject.Object {
     if (success) {
       const windowConfigContents = imports.byteArray.toString(contents);
       Logger.trace(`${windowConfigContents}`);
-      windowProps = JSON.parse(windowConfigContents);
+      try {
+        windowProps = JSON.parse(windowConfigContents);
+        if (!Array.isArray(windowProps?.overrides)) throw new Error("no overrides list");
+      } catch (e) {
+        // An empty or broken file mustn't stop Forge from starting (#415): use the default
+        // rules. Forge rewrites the file on the next change of the rules (e.g. a window closing),
+        // so keep a copy of it first.
+        let backup = "";
+        if (windowConfigContents.trim()) {
+          try {
+            const backupFile = Gio.File.new_for_path(`${windowConfigFile.get_path()}.bak`);
+            windowConfigFile.copy(backupFile, Gio.FileCopyFlags.OVERWRITE, null, null);
+            backup = `; it was copied to ${backupFile.get_path()}`;
+          } catch (copyError) {
+            backup = `; it couldn't be copied (${copyError.message})`;
+          }
+        }
+        console.warn(
+          `Forge: ${windowConfigFile.get_path()} is not valid (${e.message}); ` +
+            `using the default window rules${backup}`
+        );
+        windowProps = this.loadDefaultWindowConfigContents();
+      }
     }
     return windowProps;
   }