diff --git a/lib/fs.js b/lib/fs.js
index 58704e529747b2..a17563038058b1 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -1619,7 +1619,8 @@ function ReadStream(path, options) {
     options = {};
   else if (typeof options === 'string')
     options = { encoding: options };
-  else if (options === null || typeof options !== 'object')
+  else if (options === null ||
+           typeof options !== 'object' && typeof options !== 'function')
     throw new TypeError('options must be a string or an object');
 
   // a little bit bigger buffer and water marks by default
@@ -1790,7 +1791,8 @@ function WriteStream(path, options) {
     options = {};
   else if (typeof options === 'string')
     options = { encoding: options };
-  else if (options === null || typeof options !== 'object')
+  else if (options === null ||
+           typeof options !== 'object' && typeof options !== 'function')
     throw new TypeError('options must be a string or an object');
 
   options = Object.create(options);