diff --git a/chai.js b/chai.js
index 67b70508c..0c5868deb 100644
--- a/chai.js
+++ b/chai.js
@@ -14,7 +14,7 @@ var used = [];
  * Chai version
  */
 
-exports.version = '4.1.0';
+exports.version = '4.1.1';
 
 /*!
  * Assertion Error
@@ -830,53 +830,18 @@ module.exports = function (chai, _) {
 
   function include (val, msg) {
     if (msg) flag(this, 'message', msg);
-
-    _.expectTypes(this, [
-      'array', 'object', 'string',
-      'map', 'set', 'weakset',
-    ]);
-
+    
     var obj = flag(this, 'object')
-      , objType = _.type(obj).toLowerCase();
-
-    // This block is for asserting a subset of properties in an object.
-    if (objType === 'object') {
-      var props = Object.keys(val)
-        , negate = flag(this, 'negate')
-        , firstErr = null
-        , numErrs = 0;
-
-      props.forEach(function (prop) {
-        var propAssertion = new Assertion(obj);
-        _.transferFlags(this, propAssertion, true);
-        flag(propAssertion, 'lockSsfi', true);
-
-        if (!negate || props.length === 1) {
-          propAssertion.property(prop, val[prop]);
-          return;
-        }
-
-        try {
-          propAssertion.property(prop, val[prop]);
-        } catch (err) {
-          if (!_.checkError.compatibleConstructor(err, AssertionError)) throw err;
-          if (firstErr === null) firstErr = err;
-          numErrs++;
-        }
-      }, this);
-
-      // When validating .not.include with multiple properties, we only want
-      // to throw an assertion error if all of the properties are included,
-      // in which case we throw the first property assertion error that we
-      // encountered.
-      if (negate && props.length > 1 && numErrs === props.length) throw firstErr;
+      , objType = _.type(obj).toLowerCase()
+      , flagMsg = flag(this, 'message')
+      , negate = flag(this, 'negate')
+      , ssfi = flag(this, 'ssfi')
+      , isDeep = flag(this, 'deep')
+      , descriptor = isDeep ? 'deep ' : '';
 
-      return;
-    }
+    flagMsg = flagMsg ? flagMsg + ': ' : '';
 
-    var isDeep = flag(this, 'deep')
-      , descriptor = isDeep ? 'deep ' : ''
-      , included = false;
+    var included = false;
 
     switch (objType) {
       case 'string':
@@ -885,10 +850,6 @@ module.exports = function (chai, _) {
 
       case 'weakset':
         if (isDeep) {
-          var flagMsg = flag(this, 'message')
-            , ssfi = flag(this, 'ssfi');
-          flagMsg = flagMsg ? flagMsg + ': ' : '';
-
           throw new AssertionError(
             flagMsg + 'unable to use .deep.include with WeakSet',
             undefined,
@@ -925,6 +886,53 @@ module.exports = function (chai, _) {
           included = obj.indexOf(val) !== -1;
         }
         break;
+
+      default:
+        // This block is for asserting a subset of properties in an object.
+        // `_.expectTypes` isn't used here because `.include` should work with
+        // objects with a custom `@@toStringTag`.
+        if (val !== Object(val)) {
+          throw new AssertionError(
+            flagMsg + 'object tested must be an array, a map, an object,'
+              + ' a set, a string, or a weakset, but ' + objType + ' given',
+            undefined,
+            ssfi
+          );
+        }
+
+        var props = Object.keys(val)
+          , firstErr = null
+          , numErrs = 0;
+  
+        props.forEach(function (prop) {
+          var propAssertion = new Assertion(obj);
+          _.transferFlags(this, propAssertion, true);
+          flag(propAssertion, 'lockSsfi', true);
+  
+          if (!negate || props.length === 1) {
+            propAssertion.property(prop, val[prop]);
+            return;
+          }
+  
+          try {
+            propAssertion.property(prop, val[prop]);
+          } catch (err) {
+            if (!_.checkError.compatibleConstructor(err, AssertionError)) {
+              throw err;
+            }
+            if (firstErr === null) firstErr = err;
+            numErrs++;
+          }
+        }, this);
+  
+        // When validating .not.include with multiple properties, we only want
+        // to throw an assertion error if all of the properties are included,
+        // in which case we throw the first property assertion error that we
+        // encountered.
+        if (negate && props.length > 1 && numErrs === props.length) {
+          throw firstErr;
+        }
+        return;
     }
 
     // Assert inclusion in collection or substring in a string.
@@ -1962,28 +1970,25 @@ module.exports = function (chai, _) {
     var target = flag(this, 'object')
     var ssfi = flag(this, 'ssfi');
     var flagMsg = flag(this, 'message');
-    var validInstanceOfTarget = constructor === Object(constructor) && (
-        typeof constructor === 'function' ||
-        (typeof Symbol !== 'undefined' &&
-         typeof Symbol.hasInstance !== 'undefined' &&
-         Symbol.hasInstance in constructor)
-    );
 
-    if (!validInstanceOfTarget) {
-      flagMsg = flagMsg ? flagMsg + ': ' : '';
-      var constructorType = constructor === null ? 'null' : typeof constructor;
-      throw new AssertionError(
-        flagMsg + 'The instanceof assertion needs a constructor but ' + constructorType + ' was given.',
-        undefined,
-        ssfi
-      );
+    try {
+      var isInstanceOf = target instanceof constructor;
+    } catch (err) {
+      if (err instanceof TypeError) {
+        flagMsg = flagMsg ? flagMsg + ': ' : '';
+        throw new AssertionError(
+          flagMsg + 'The instanceof assertion needs a constructor but '
+            + _.type(constructor) + ' was given.',
+          undefined,
+          ssfi
+        );
+      }
+      throw err;
     }
 
-    var isInstanceOf = target instanceof constructor
-
     var name = _.getName(constructor);
     if (name === null) {
-        name = 'an unnamed constructor';
+      name = 'an unnamed constructor';
     }
 
     this.assert(
@@ -5762,10 +5767,10 @@ module.exports = function (chai, util) {
    * You can also provide a single object instead of a `keys` array and its keys
    * will be used as the expected set of keys.
    *
-   *     assert.hasAnyKey({foo: 1, bar: 2, baz: 3}, ['foo', 'iDontExist', 'baz']);
-   *     assert.hasAnyKey({foo: 1, bar: 2, baz: 3}, {foo: 30, iDontExist: 99, baz: 1337]);
-   *     assert.hasAnyKey(new Map([[{foo: 1}, 'bar'], ['key', 'value']]), [{foo: 1}, 'thisKeyDoesNotExist']);
-   *     assert.hasAnyKey(new Set([{foo: 'bar'}, 'anotherKey'], [{foo: 'bar'}, 'thisKeyDoesNotExist']);
+   *     assert.hasAnyKeys({foo: 1, bar: 2, baz: 3}, ['foo', 'iDontExist', 'baz']);
+   *     assert.hasAnyKeys({foo: 1, bar: 2, baz: 3}, {foo: 30, iDontExist: 99, baz: 1337});
+   *     assert.hasAnyKeys(new Map([[{foo: 1}, 'bar'], ['key', 'value']]), [{foo: 1}, 'key']);
+   *     assert.hasAnyKeys(new Set([{foo: 'bar'}, 'anotherKey']), [{foo: 'bar'}, 'anotherKey']);
    *
    * @name hasAnyKeys
    * @param {Mixed} object
diff --git a/lib/chai.js b/lib/chai.js
index c1afbee92..2ad493bcb 100644
--- a/lib/chai.js
+++ b/lib/chai.js
@@ -10,7 +10,7 @@ var used = [];
  * Chai version
  */
 
-exports.version = '4.1.0';
+exports.version = '4.1.1';
 
 /*!
  * Assertion Error
diff --git a/package.json b/package.json
index d0c86fc69..b56609084 100644
--- a/package.json
+++ b/package.json
@@ -17,7 +17,7 @@
     "Veselin Todorov <hi@vesln.com>",
     "John Firebaugh <john.firebaugh@gmail.com>"
   ],
-  "version": "4.1.0",
+  "version": "4.1.1",
   "repository": {
     "type": "git",
     "url": "https://github.com/chaijs/chai"