diff --git a/tests/cases/fourslash/javaScriptClass1.ts b/tests/cases/fourslash/javaScriptClass1.ts
index 117fc5be9be..19f7a39b615 100644
--- a/tests/cases/fourslash/javaScriptClass1.ts
+++ b/tests/cases/fourslash/javaScriptClass1.ts
@@ -8,7 +8,7 @@
 //// class Foo {
 ////    constructor() {
 ////        this.bar = 'world';
-////        this.thing = 42;
+////        this.thing = () => 0;
 ////        this.union = 'foo';
 ////        this.union = 100;
 ////    }
@@ -25,7 +25,6 @@ verify.completionListContains("union", /*displayText*/ undefined, /*documentatio
 
 edit.insert('bar.');
 verify.completionListContains("substr", /*displayText*/ undefined, /*documentation*/ undefined, "method");
-
 edit.backspace('bar.'.length);
 
 edit.insert('union.');
diff --git a/tests/cases/fourslash/javaScriptClass4.ts b/tests/cases/fourslash/javaScriptClass4.ts
new file mode 100644
index 00000000000..1148d5f320e
--- /dev/null
+++ b/tests/cases/fourslash/javaScriptClass4.ts
@@ -0,0 +1,22 @@
+///<reference path="fourslash.ts" />
+
+// Classes have their shape inferred from assignments
+// to properties of 'this' in the constructor
+
+// @allowNonTsExtensions: true
+// @Filename: Foo.js
+//// class Foo {
+////    constructor() {
+////        /**
+////          * @type {string}
+////        */
+////        this.baz = null;
+////    }
+//// }
+//// var x = new Foo();
+//// x/**/
+
+goTo.marker();
+edit.insert('.baz.');
+verify.completionListContains("substr", /*displayText*/ undefined, /*documentation*/ undefined, "method");
+