diff --git a/lib/fs.js b/lib/fs.js
index 0fe1be4c456070..20b6274a666248 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -44,9 +44,24 @@ const isWindows = process.platform === 'win32';
 const DEBUG = process.env.NODE_DEBUG && /fs/.test(process.env.NODE_DEBUG);
 const errnoException = util._errnoException;
 
-function throwOptionsError(options) {
-  throw new TypeError('Expected options to be either an object or a string, ' +
-    'but got ' + typeof options + ' instead');
+function getOptions(options, defaultOptions) {
+  if (options === null || options === undefined ||
+      typeof options === 'function') {
+    return defaultOptions;
+  }
+
+  if (typeof options === 'string') {
+    defaultOptions = util._extend({}, defaultOptions);
+    defaultOptions.encoding = options;
+    options = defaultOptions;
+  } else if (typeof options !== 'object') {
+    throw new TypeError('"options" must be a string or an object, got ' +
+                        typeof options + ' instead.');
+  }
+
+  if (options.encoding !== 'buffer')
+    assertEncoding(options.encoding);
+  return options;
 }
 
 function rethrow() {
@@ -236,26 +251,14 @@ fs.existsSync = function(path) {
   }
 };
 
-fs.readFile = function(path, options, callback_) {
-  var callback = maybeCallback(arguments[arguments.length - 1]);
-
-  if (!options || typeof options === 'function') {
-    options = { encoding: null, flag: 'r' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, flag: 'r' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
-
-  var encoding = options.encoding;
-  assertEncoding(encoding);
-
-  var flag = options.flag || 'r';
+fs.readFile = function(path, options, callback) {
+  callback = maybeCallback(arguments[arguments.length - 1]);
+  options = getOptions(options, { flag: 'r' });
 
   if (!nullCheck(path, callback))
     return;
 
-  var context = new ReadFileContext(callback, encoding);
+  var context = new ReadFileContext(callback, options.encoding);
   context.isUserFd = isFd(path); // file descriptor ownership
   var req = new FSReqWrap();
   req.context = context;
@@ -269,7 +272,7 @@ fs.readFile = function(path, options, callback_) {
   }
 
   binding.open(pathModule._makeLong(path),
-               stringToFlags(flag),
+               stringToFlags(options.flag || 'r'),
                0o666,
                req);
 };
@@ -460,20 +463,9 @@ function tryReadSync(fd, isUserFd, buffer, pos, len) {
 }
 
 fs.readFileSync = function(path, options) {
-  if (!options) {
-    options = { encoding: null, flag: 'r' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, flag: 'r' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
-
-  var encoding = options.encoding;
-  assertEncoding(encoding);
-
-  var flag = options.flag || 'r';
+  options = getOptions(options, { flag: 'r' });
   var isUserFd = isFd(path); // file descriptor ownership
-  var fd = isUserFd ? path : fs.openSync(path, flag, 0o666);
+  var fd = isUserFd ? path : fs.openSync(path, options.flag || 'r', 0o666);
 
   var st = tryStatSync(fd, isUserFd);
   var size = st.isFile() ? st.size : 0;
@@ -517,7 +509,7 @@ fs.readFileSync = function(path, options) {
     buffer = buffer.slice(0, pos);
   }
 
-  if (encoding) buffer = buffer.toString(encoding);
+  if (options.encoding) buffer = buffer.toString(options.encoding);
   return buffer;
 };
 
@@ -899,17 +891,8 @@ fs.mkdirSync = function(path, mode) {
 };
 
 fs.readdir = function(path, options, callback) {
-  options = options || {};
-  if (typeof options === 'function') {
-    callback = options;
-    options = {};
-  } else if (typeof options === 'string') {
-    options = {encoding: options};
-  }
-  if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
-
-  callback = makeCallback(callback);
+  callback = makeCallback(typeof options === 'function' ? options : callback);
+  options = getOptions(options, {});
   if (!nullCheck(path, callback)) return;
   var req = new FSReqWrap();
   req.oncomplete = callback;
@@ -917,11 +900,7 @@ fs.readdir = function(path, options, callback) {
 };
 
 fs.readdirSync = function(path, options) {
-  options = options || {};
-  if (typeof options === 'string')
-    options = {encoding: options};
-  if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
+  options = getOptions(options, {});
   nullCheck(path);
   return binding.readdir(pathModule._makeLong(path), options.encoding);
 };
@@ -963,16 +942,8 @@ fs.statSync = function(path) {
 };
 
 fs.readlink = function(path, options, callback) {
-  options = options || {};
-  if (typeof options === 'function') {
-    callback = options;
-    options = {};
-  } else if (typeof options === 'string') {
-    options = {encoding: options};
-  }
-  if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
-  callback = makeCallback(callback);
+  callback = makeCallback(typeof options === 'function' ? options : callback);
+  options = getOptions(options, {});
   if (!nullCheck(path, callback)) return;
   var req = new FSReqWrap();
   req.oncomplete = callback;
@@ -980,11 +951,7 @@ fs.readlink = function(path, options, callback) {
 };
 
 fs.readlinkSync = function(path, options) {
-  options = options || {};
-  if (typeof options === 'string')
-    options = {encoding: options};
-  if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
+  options = getOptions(options, {});
   nullCheck(path);
   return binding.readlink(pathModule._makeLong(path), options.encoding);
 };
@@ -1255,20 +1222,10 @@ function writeAll(fd, isUserFd, buffer, offset, length, position, callback_) {
   });
 }
 
-fs.writeFile = function(path, data, options, callback_) {
-  var callback = maybeCallback(arguments[arguments.length - 1]);
-
-  if (!options || typeof options === 'function') {
-    options = { encoding: 'utf8', mode: 0o666, flag: 'w' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, mode: 0o666, flag: 'w' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
-
-  assertEncoding(options.encoding);
-
-  var flag = options.flag || 'w';
+fs.writeFile = function(path, data, options, callback) {
+  callback = maybeCallback(arguments[arguments.length - 1]);
+  options = getOptions(options, { encoding: 'utf8', mode: 0o666, flag: 'w' });
+  const flag = options.flag || 'w';
 
   if (isFd(path)) {
     writeFd(path, true);
@@ -1293,17 +1250,9 @@ fs.writeFile = function(path, data, options, callback_) {
 };
 
 fs.writeFileSync = function(path, data, options) {
-  if (!options) {
-    options = { encoding: 'utf8', mode: 0o666, flag: 'w' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, mode: 0o666, flag: 'w' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
-
-  assertEncoding(options.encoding);
+  options = getOptions(options, { encoding: 'utf8', mode: 0o666, flag: 'w' });
+  const flag = options.flag || 'w';
 
-  var flag = options.flag || 'w';
   var isUserFd = isFd(path); // file descriptor ownership
   var fd = isUserFd ? path : fs.openSync(path, flag, options.mode);
 
@@ -1327,16 +1276,9 @@ fs.writeFileSync = function(path, data, options) {
   }
 };
 
-fs.appendFile = function(path, data, options, callback_) {
-  var callback = maybeCallback(arguments[arguments.length - 1]);
-
-  if (!options || typeof options === 'function') {
-    options = { encoding: 'utf8', mode: 0o666, flag: 'a' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, mode: 0o666, flag: 'a' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
+fs.appendFile = function(path, data, options, callback) {
+  callback = maybeCallback(arguments[arguments.length - 1]);
+  options = getOptions(options, { encoding: 'utf8', mode: 0o666, flag: 'a' });
 
   if (!options.flag)
     options = util._extend({ flag: 'a' }, options);
@@ -1349,13 +1291,7 @@ fs.appendFile = function(path, data, options, callback_) {
 };
 
 fs.appendFileSync = function(path, data, options) {
-  if (!options) {
-    options = { encoding: 'utf8', mode: 0o666, flag: 'a' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, mode: 0o666, flag: 'a' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
+  options = getOptions(options, { encoding: 'utf8', mode: 0o666, flag: 'a' });
 
   if (!options.flag)
     options = util._extend({ flag: 'a' }, options);
@@ -1414,15 +1350,10 @@ FSWatcher.prototype.close = function() {
 fs.watch = function(filename, options, listener) {
   nullCheck(filename);
 
-  options = options || {};
   if (typeof options === 'function') {
     listener = options;
-    options = {};
-  } else if (typeof options === 'string') {
-    options = {encoding: options};
   }
-  if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
+  options = getOptions(options, {});
 
   if (options.persistent === undefined) options.persistent = true;
   if (options.recursive === undefined) options.recursive = false;
@@ -1569,12 +1500,7 @@ function encodeRealpathResult(result, options, err) {
 const realpathCacheKey = fs.realpathCacheKey = Symbol('realpathCacheKey');
 
 fs.realpathSync = function realpathSync(p, options) {
-  if (!options)
-    options = {};
-  else if (typeof options === 'string')
-    options = {encoding: options};
-  else if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
+  options = getOptions(options, {});
   nullCheck(p);
 
   p = p.toString('utf8');
@@ -1675,20 +1601,8 @@ fs.realpathSync = function realpathSync(p, options) {
 
 
 fs.realpath = function realpath(p, options, callback) {
-  if (typeof callback !== 'function') {
-    callback = maybeCallback(options);
-    options = {};
-  }
-
-  if (!options) {
-    options = {};
-  } else if (typeof options === 'function') {
-    options = {};
-  } else if (typeof options === 'string') {
-    options = {encoding: options};
-  } else if (typeof options !== 'object') {
-    throw new TypeError('"options" must be a string or an object');
-  }
+  callback = maybeCallback(typeof options === 'function' ? options : callback);
+  options = getOptions(options, {});
   if (!nullCheck(p, callback))
     return;
 
@@ -1797,20 +1711,10 @@ fs.realpath = function realpath(p, options, callback) {
 };
 
 fs.mkdtemp = function(prefix, options, callback) {
+  callback = makeCallback(typeof options === 'function' ? options : callback);
+  options = getOptions(options, {});
   if (!prefix || typeof prefix !== 'string')
     throw new TypeError('filename prefix is required');
-
-  options = options || {};
-  if (typeof options === 'function') {
-    callback = options;
-    options = {};
-  } else if (typeof options === 'string') {
-    options = {encoding: options};
-  }
-  if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
-
-  callback = makeCallback(callback);
   if (!nullCheck(prefix, callback)) {
     return;
   }
@@ -1825,14 +1729,8 @@ fs.mkdtemp = function(prefix, options, callback) {
 fs.mkdtempSync = function(prefix, options) {
   if (!prefix || typeof prefix !== 'string')
     throw new TypeError('filename prefix is required');
-
-  options = options || {};
-  if (typeof options === 'string')
-    options = {encoding: options};
-  if (typeof options !== 'object')
-    throw new TypeError('"options" must be a string or an object');
+  options = getOptions(options, {});
   nullCheck(prefix);
-
   return binding.mkdtemp(prefix + 'XXXXXX', options.encoding);
 };
 
@@ -1856,15 +1754,8 @@ function ReadStream(path, options) {
   if (!(this instanceof ReadStream))
     return new ReadStream(path, options);
 
-  if (options === undefined)
-    options = {};
-  else if (typeof options === 'string')
-    options = { encoding: options };
-  else if (options === null || typeof options !== 'object')
-    throw new TypeError('"options" argument must be a string or an object');
-
   // a little bit bigger buffer and water marks by default
-  options = Object.create(options);
+  options = Object.create(getOptions(options, {}));
   if (options.highWaterMark === undefined)
     options.highWaterMark = 64 * 1024;
 
@@ -2030,14 +1921,7 @@ function WriteStream(path, options) {
   if (!(this instanceof WriteStream))
     return new WriteStream(path, options);
 
-  if (options === undefined)
-    options = {};
-  else if (typeof options === 'string')
-    options = { encoding: options };
-  else if (options === null || typeof options !== 'object')
-    throw new TypeError('"options" argument must be a string or an object');
-
-  options = Object.create(options);
+  options = Object.create(getOptions(options, {}));
 
   Writable.call(this, options);
 
diff --git a/test/parallel/test-fs-read-stream-throw-type-error.js b/test/parallel/test-fs-read-stream-throw-type-error.js
index 81f924d355b91c..bc1fca3a3c3e6a 100644
--- a/test/parallel/test-fs-read-stream-throw-type-error.js
+++ b/test/parallel/test-fs-read-stream-throw-type-error.js
@@ -9,6 +9,9 @@ const example = path.join(common.fixturesDir, 'x.txt');
 assert.doesNotThrow(function() {
   fs.createReadStream(example, undefined);
 });
+assert.doesNotThrow(function() {
+  fs.createReadStream(example, null);
+});
 assert.doesNotThrow(function() {
   fs.createReadStream(example, 'utf8');
 });
@@ -16,18 +19,15 @@ assert.doesNotThrow(function() {
   fs.createReadStream(example, {encoding: 'utf8'});
 });
 
-assert.throws(function() {
-  fs.createReadStream(example, null);
-}, /"options" argument must be a string or an object/);
 assert.throws(function() {
   fs.createReadStream(example, 123);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);
 assert.throws(function() {
   fs.createReadStream(example, 0);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);
 assert.throws(function() {
   fs.createReadStream(example, true);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);
 assert.throws(function() {
   fs.createReadStream(example, false);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);
diff --git a/test/parallel/test-fs-write-stream-throw-type-error.js b/test/parallel/test-fs-write-stream-throw-type-error.js
index 007ac03f1bb342..996b22119cda5e 100644
--- a/test/parallel/test-fs-write-stream-throw-type-error.js
+++ b/test/parallel/test-fs-write-stream-throw-type-error.js
@@ -11,6 +11,9 @@ common.refreshTmpDir();
 assert.doesNotThrow(function() {
   fs.createWriteStream(example, undefined);
 });
+assert.doesNotThrow(function() {
+  fs.createWriteStream(example, null);
+});
 assert.doesNotThrow(function() {
   fs.createWriteStream(example, 'utf8');
 });
@@ -18,18 +21,15 @@ assert.doesNotThrow(function() {
   fs.createWriteStream(example, {encoding: 'utf8'});
 });
 
-assert.throws(function() {
-  fs.createWriteStream(example, null);
-}, /"options" argument must be a string or an object/);
 assert.throws(function() {
   fs.createWriteStream(example, 123);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);
 assert.throws(function() {
   fs.createWriteStream(example, 0);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);
 assert.throws(function() {
   fs.createWriteStream(example, true);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);
 assert.throws(function() {
   fs.createWriteStream(example, false);
-}, /"options" argument must be a string or an object/);
+}, /"options" must be a string or an object/);