diff --git a/video_prediction_tools/postprocess/plot_ambs_forecast.py b/video_prediction_tools/postprocess/plot_ambs_forecast.py
index 83b1c8ff89eabb1e6850e638db5f2f88ff624ead..1f7da969d9b643663142dd6aaa18502235668eab 100644
--- a/video_prediction_tools/postprocess/plot_ambs_forecast.py
+++ b/video_prediction_tools/postprocess/plot_ambs_forecast.py
@@ -123,7 +123,7 @@ def main(args):
     filename = args.filename
     fhh = args.forecast_hour
 
-    if os.path.isfile(filename):
+    if not os.path.isfile(filename):
         raise FileNotFoundError("Could not find the indictaed netCDF-file '{0}'".format(filename))
 
     with xr.open_dataset(filename) as dfile: