diff --git a/source-map-support.js b/source-map-support.js
index 5af4780..236bb03 100644
--- a/source-map-support.js
+++ b/source-map-support.js
@@ -4,6 +4,10 @@ var path = require('path');
 var fs;
 try {
   fs = require('fs');
+  if (!fs.readFileSync || !fs.readFileSync) {
+    // fs doesn't have all methods we need
+    fs = null;
+  }
 } catch (err) {
   /* nop */
 }