diff --git a/chai-immutable.js b/chai-immutable.js
index 1adb128..eee10e1 100644
--- a/chai-immutable.js
+++ b/chai-immutable.js
@@ -46,7 +46,7 @@
       return function () {
         var obj = this._obj;
 
-        if (obj && obj instanceof Collection) {
+        if (Immutable.Iterable.isIterable(obj)) {
           var size = obj.size;
           new Assertion(size).a('number');
 
@@ -96,7 +96,7 @@
       return function (collection) {
         var obj = this._obj;
 
-        if (obj && obj instanceof Collection) {
+        if (Immutable.Iterable.isIterable(obj)) {
           this.assert(
             Immutable.is(obj, collection),
             'expected #{act} to equal #{exp}',
@@ -141,7 +141,7 @@
       return function (val) {
         var obj = this._obj;
 
-        if (obj && obj instanceof Collection) {
+        if (Immutable.Iterable.isIterable(obj)) {
           this.assert(
             obj.includes(val),
             'expected #{act} to include #{exp}',
@@ -483,7 +483,7 @@
       // It seems like we shouldn't actually need this check, however,
       // `assert.equal` actually behaves differently than its BDD counterpart!
       // Namely, the BDD version is strict while the "assert" one isn't.
-      if (actual instanceof Collection) {
+      if (Immutable.Iterable.isIterable(actual)) {
         return new Assertion(actual).equal(expected);
       }
       else return originalEqual(actual, expected);
@@ -509,7 +509,7 @@
      */
 
     assert.notEqual = function (actual, expected) {
-      if (actual instanceof Collection) {
+      if (Immutable.Iterable.isIterable(actual)) {
         return new Assertion(actual).not.equal(expected);
       }
       else return originalNotEqual(actual, expected);
diff --git a/test/test.js b/test/test.js
index c982f3f..89b88bc 100644
--- a/test/test.js
+++ b/test/test.js
@@ -5,6 +5,7 @@ if (!chai) {
   var chai = require('chai');
   var chaiImmutable = require('../chai-immutable');
   var Immutable = require('immutable');
+  var otherImmutable = require('../node_modules/immutable/dist/immutable.min.js');
 
   chai.use(chaiImmutable);
   typeEnv = 'Node.js';
@@ -45,6 +46,8 @@ describe('chai-immutable (' + typeEnv + ')', function () {
     list: List.of(42)
   });
 
+  var otherImmutableList = otherImmutable.List.of(1, 2, 3);
+
   describe('BDD interface', function () {
     describe('empty property', function () {
       it('should pass given an empty collection', function () {
@@ -68,6 +71,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
       it('should fail using `not` given an empty collection', function () {
         fail(function () { expect(new List()).to.not.be.empty; });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          expect(otherImmutable.List()).to.be.empty;
+        });
+      }
     });
 
     describe('equal method', function () {
@@ -162,6 +171,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
         fail(function () { expect(deepMap).to.not.eqls(sameDeepMap); });
         fail(function () { expect(deepMap).to.not.deep.equal(sameDeepMap); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          expect(otherImmutableList).to.equal(otherImmutable.List.of(1, 2, 3));
+        });
+      }
     });
 
     describe('include method', function () {
@@ -376,6 +391,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
         fail(function () { expect(map).to.contain.key('z'); });
         fail(function () { expect(obj).to.contain.key('z'); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          expect(otherImmutable.Map({ x: 1 })).to.have.key('x');
+        });
+      }
     });
 
     describe('size method', function () {
@@ -399,6 +420,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
       it('should fail using `not` given the right size', function () {
         fail(function () { expect(list3).to.not.have.size(3); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          expect(otherImmutableList).to.have.size(3);
+        });
+      }
     });
 
     describe('size property', function () {
@@ -530,6 +557,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
       it('most should fail using `not` given a bad max size', function () {
         fail(function () { expect(list3).to.not.have.size.of.at.most(42); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          expect(otherImmutableList).to.have.size.above(2);
+        });
+      }
     });
   });
 
@@ -568,6 +601,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
       it('should fail given deeply different values', function () {
         fail(function () { assert.equal(deepMap, differentDeepMap); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          assert.equal(otherImmutableList, otherImmutable.List.of(1, 2, 3));
+        });
+      }
     });
 
     describe('notEqual assertion', function () {
@@ -595,6 +634,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
       it('should fail given deeply equal values', function () {
         fail(function () { assert.notEqual(deepMap, sameDeepMap); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          assert.notEqual(otherImmutableList, otherImmutable.List.of());
+        });
+      }
     });
 
     describe('unoverridden strictEqual and deepEqual assertions', function () {
@@ -617,6 +662,13 @@ describe('chai-immutable (' + typeEnv + ')', function () {
         fail(function () { assert.strictEqual(deepMap, differentDeepMap); });
         fail(function () { assert.deepEqual(deepMap, differentDeepMap); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          assert.strictEqual(otherImmutableList, otherImmutable.List.of(1, 2, 3));
+          assert.deepEqual(otherImmutableList, otherImmutable.List.of(1, 2, 3));
+        });
+      }
     });
 
     describe('unoverridden notStrictEqual and notDeepEqual assertions', function () {
@@ -639,6 +691,13 @@ describe('chai-immutable (' + typeEnv + ')', function () {
         fail(function () { assert.notStrictEqual(deepMap, sameDeepMap); });
         fail(function () { assert.notDeepEqual(deepMap, sameDeepMap); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          assert.notStrictEqual(otherImmutableList, otherImmutable.List());
+          assert.notDeepEqual(otherImmutableList, otherImmutable.List());
+        });
+      }
     });
 
     describe('sizeOf assertion', function () {
@@ -653,6 +712,12 @@ describe('chai-immutable (' + typeEnv + ')', function () {
       it('should fail given the wrong size', function () {
         fail(function () { assert.sizeOf(list3, 42); });
       });
+
+      if (typeEnv === 'Node.js') {
+        it('should work if using different copies of Immtuable', function () {
+          assert.sizeOf(otherImmutableList, 3);
+        });
+      }
     });
   });
 });