diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 551f428ca9a..86754ff93d0 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2766,7 +2766,10 @@ namespace ts {
         }
 
         function getBaseTypeNodeOfClass(type: InterfaceType): ExpressionWithTypeArguments {
-            return getClassExtendsHeritageClauseElement(<ClassLikeDeclaration>type.symbol.valueDeclaration);
+            let classDeclaration = getDeclarationOfKind(type.symbol, SyntaxKind.ClassDeclaration);
+            if (classDeclaration) {
+                return getClassExtendsHeritageClauseElement(classDeclaration as ClassLikeDeclaration);
+            }
         }
 
         function getConstructorsForTypeArguments(type: ObjectType, typeArgumentNodes: TypeNode[]): Signature[] {