diff --git a/lib/readline-sync.js b/lib/readline-sync.js
index cc54f25..587e81f 100644
--- a/lib/readline-sync.js
+++ b/lib/readline-sync.js
@@ -266,7 +266,7 @@ function readlineExt(options) {
     try {
       res.input = childProc.execFileSync(extHostPath, hostArgs, execOptions);
     } catch (e) { // non-zero exit code
-      extMessage = e.stderr.trim();
+      extMessage = e.stderr ? (e.stderr + '').trim() : '';
       res.error = new Error(DEFAULT_ERR_MSG + (extMessage ? '\n' + extMessage : ''));
       res.error.method = 'execFileSync';
       res.error.program = extHostPath;