diff --git a/chai-iterator.js b/chai-iterator.js
index be9bb9b..7d3c85f 100644
--- a/chai-iterator.js
+++ b/chai-iterator.js
@@ -63,10 +63,10 @@
 
   Assertion.addProperty('for', noop);
 
-  Assertion.overwriteMethod('lengthOf', function(_super) {
+  Assertion.overwriteChainableMethod('lengthOf', function(_super) {
     return function(exp) {
-        if (utils.flag(this, 'iterate')) {
-          var len = iterableLength(this._obj, exp);
+      if (utils.flag(this, 'iterate')) {
+        var len = iterableLength(this._obj, exp);
 
         this.assert(
           len === exp,
@@ -80,6 +80,10 @@
         _super.apply(this, arguments);
       }
     };
+  }, function(_super) {
+    return function() {
+      _super.apply(this);
+    };
   });
 
   Assertion.overwriteMethod('above', function(_super) {
diff --git a/package.json b/package.json
index e8caf3d..dd94da8 100644
--- a/package.json
+++ b/package.json
@@ -41,11 +41,11 @@
   },
   "homepage": "https://github.com/mcmath/chai-iterator",
   "peerDependencies": {
-    "chai": "3.x"
+    "chai": "4.x"
   },
   "devDependencies": {
     "@types/chai": "^3.4.35",
-    "chai": "^3.5.0",
+    "chai": "^4.1.2",
     "coffee-script": "^1.12.4",
     "core-js": "^2.4.1",
     "coveralls": "^2.12.0",