diff --git a/compat/src/index.js b/compat/src/index.js
index 999c8e24f59..2855eb5cfc8 100644
--- a/compat/src/index.js
+++ b/compat/src/index.js
@@ -303,8 +303,8 @@ let classNameDescriptor = {
  * @returns {boolean}
  */
 function shallowDiffers(a, b) {
-	for (let i in a) if (!(i in b)) return true;
-	for (let i in b) if (a[i]!==b[i]) return true;
+	for (let i in a) if (i !== '__source' && !(i in b)) return true;
+	for (let i in b) if (i !== '__source' && a[i]!==b[i]) return true;
 	return false;
 }
 
diff --git a/compat/test/browser/component.test.js b/compat/test/browser/component.test.js
index 95538707e7e..0138067db82 100644
--- a/compat/test/browser/component.test.js
+++ b/compat/test/browser/component.test.js
@@ -95,6 +95,34 @@ describe('components', () => {
 			expect(spy).to.be.calledWithMatch(expected, expected);
 		});
 
+		it('should ignore the __source variable', () => {
+			const pureSpy = sinon.spy();
+			const appSpy = sinon.spy();
+			let set;
+			class Pure extends React.PureComponent {
+				render()  {
+					pureSpy();
+					return <div>Static</div>;
+				}
+			}
+
+			const App = () => {
+				const [, setState] = React.useState(0);
+				appSpy();
+				set = setState;
+				return <Pure __source={{}} />;
+			};
+
+			React.render(<App />, scratch);
+			expect(appSpy).to.be.calledOnce;
+			expect(pureSpy).to.be.calledOnce;
+
+			set(1);
+			rerender();
+			expect(appSpy).to.be.calledTwice;
+			expect(pureSpy).to.be.calledOnce;
+		});
+
 		it('should only re-render when props or state change', () => {
 			class C extends React.PureComponent {
 				render() {