diff --git a/src/index.spec.ts b/src/index.spec.ts
index 725bb8b1d..29b90495a 100644
--- a/src/index.spec.ts
+++ b/src/index.spec.ts
@@ -596,7 +596,7 @@ describe('ts-node', function () {
             return _compile.call(this, code, fileName)
           }
 
-          return old(m, fileName)
+          return old!(m, fileName)
         }
       })