diff --git a/signalgen.py b/signalgen.py
index 4a82f7f..916be76 100644
--- a/signalgen.py
+++ b/signalgen.py
@@ -3,8 +3,9 @@
 import logging
 from os import path
 from argparse import ArgumentDefaultsHelpFormatter, ArgumentParser
-import numpy as np
+from typing import Union
 
+import numpy as np
 import matplotlib.pyplot as plt
 from jess.dispersion import dedisperse
 from jess.fitters import median_fitter