diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 9efaf72c03a..3abf271a57b 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -4979,7 +4979,7 @@ namespace ts {
         }
 
         function getTypeReferenceArity(type: TypeReference): number {
-            return type.target.typeParameters.length;
+            return type.target.typeParameters ? type.target.typeParameters.length : 0;
         }
 
         // Get type from reference to class or interface