diff --git a/lib/cli-engine/config-array/ignore-pattern.js b/lib/cli-engine/config-array/ignore-pattern.js
index 3f28982a99c..b385aa923e9 100644
--- a/lib/cli-engine/config-array/ignore-pattern.js
+++ b/lib/cli-engine/config-array/ignore-pattern.js
@@ -38,8 +38,6 @@ const path = require("path");
 const ignore = require("ignore");
 const debug = require("debug")("eslint:ignore-pattern");
 
-// debug.enabled = true;
-
 /** @typedef {ReturnType<import("ignore").default>} Ignore */
 
 //------------------------------------------------------------------------------
@@ -73,7 +71,7 @@ function getCommonAncestorPath(sourcePaths) {
         }
     }
 
-    return result;
+    return result || path.sep;
 }
 
 /**