diff --git a/package.json b/package.json
index 9f9ad08..744df91 100644
--- a/package.json
+++ b/package.json
@@ -36,6 +36,7 @@
   "license": "MIT",
   "dependencies": {
     "lodash.compact": "^3.0.1",
+    "lodash.isplainobject": "^4.0.6",
     "lodash.omit": "^4.5.0",
     "object-values": "^1.0.0",
     "object.entries": "^1.0.3"
diff --git a/src/shallow.js b/src/shallow.js
index 2c60049..e47e774 100644
--- a/src/shallow.js
+++ b/src/shallow.js
@@ -1,4 +1,5 @@
 import compact from 'lodash.compact';
+import isPlainObject from 'lodash.isplainobject';
 import omit from 'lodash.omit';
 import entries from 'object.entries';
 import {propsOfNode} from 'enzyme/build/Utils';
@@ -18,7 +19,7 @@ function nodeToJson(node) {
             return node.map(nodeToJson);
         }
 
-        if (typeof node === 'object') {
+        if (isPlainObject(node)) {
             return entries(node).reduce((obj, [key, val]) => {
                 obj[key] = nodeToJson(val);
                 return obj;
diff --git a/test/__snapshots__/shallow.test.js.snap b/test/__snapshots__/shallow.test.js.snap
index 42984b0..057008b 100644
--- a/test/__snapshots__/shallow.test.js.snap
+++ b/test/__snapshots__/shallow.test.js.snap
@@ -96,3 +96,12 @@ exports[`test handles elements in props 1`] = `
     </BasicPure>
   } />
 `;
+
+exports[`test ignores non-plain objects 1`] = `
+<BasicPure
+  instance={
+    TestConstructor {
+      "_test": true,
+    }
+  } />
+`;
diff --git a/test/shallow.test.js b/test/shallow.test.js
index 13b7676..2c90250 100644
--- a/test/shallow.test.js
+++ b/test/shallow.test.js
@@ -68,3 +68,15 @@ it('handles elements in prop objects', () => {
 
     expect(shallowToJson(shallowed)).toMatchSnapshot();
 });
+
+it('ignores non-plain objects', () => {
+    function TestConstructor() {
+        this._test = true;
+    }
+
+    const shallowed = shallow(
+        <WrapperComponent instance={new TestConstructor()} />
+    );
+
+    expect(shallowToJson(shallowed)).toMatchSnapshot();
+});