diff --git a/src/preprocessor.ts b/src/preprocessor.ts
index 77935413c6..cccc7e7fa0 100644
--- a/src/preprocessor.ts
+++ b/src/preprocessor.ts
@@ -10,7 +10,7 @@ const babelJest = require('babel-jest')
         plugins: ['transform-es2015-modules-commonjs']
     });
 
-export function process(src, path, config, transformOptions) {
+export function process(src, path, config, transformOptions: any = {}) {
     const root = require('pkg-dir').sync();
     // transformOptions.instrument is a proxy for collectCoverage
     // https://github.com/kulshekhar/ts-jest/issues/201#issuecomment-300572902