From ea94a3430dbd7d39692578f2e80d890e5847d5ff Mon Sep 17 00:00:00 2001
From: Daniel Rosenwasser <Daniel.Rosenwasser@microsoft.com>
Date: Thu, 28 Dec 2017 15:43:20 -0800
Subject: [PATCH] Check whether we have a class before testing whether we have
 a super-class.

---
 src/compiler/checker.ts | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 82ab87d3160..af772733f05 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -15872,6 +15872,9 @@ namespace ts {
          * In that case we won't consider it used before its declaration, because it gets its value from the superclass' declaration.
          */
         function isPropertyDeclaredInAncestorClass(prop: Symbol): boolean {
+            if (!(prop.parent.flags & SymbolFlags.Class)) {
+                return false;
+            }
             let classType = getTypeOfSymbol(prop.parent) as InterfaceType;
             while (true) {
                 classType = getSuperClass(classType);