diff --git a/markdownlint-cli2.js b/markdownlint-cli2.js
index 8d01bd3..6327fa1 100755
--- a/markdownlint-cli2.js
+++ b/markdownlint-cli2.js
@@ -996,10 +996,11 @@ const main = async (params) => {
   }
   // Add stdin as a non-file input if necessary
   if (useStdin) {
+    const key = pathPosix.join(baseDir, "stdin");
     const { text } = require("node:stream/consumers");
     nonFileContents = {
       ...nonFileContents,
-      "./stdin": await text(process.stdin)
+      [key]: await text(process.stdin)
     };
   }
   // Include any file overrides or non-file content