diff --git a/src/seismic_hazard_forecasting.py b/src/seismic_hazard_forecasting.py
index 91ea5cb..edc8e5a 100644
--- a/src/seismic_hazard_forecasting.py
+++ b/src/seismic_hazard_forecasting.py
@@ -48,7 +48,7 @@ def main(catalog_file, mc_file, pdf_file, m_file, m_select, mag_label, mc, m_max
     import logging
     from base_logger import getDefaultLogger
     from timeit import default_timer as timer
-    from math import ceil, floor
+    from math import ceil, floor, isnan
     import numpy as np
     import scipy
     import obspy
@@ -501,8 +501,8 @@ verbose: {verbose}")
             iml_grid_hd[iml_grid_hd == 0.0] = np.nan  # change zeroes back to nan
 
             # trim edges so the grid is not so blocky
-            vmin_hd = min(x for x in iml_grid_hd.flatten() if not math.isnan(x))
-            vmax_hd = max(x for x in iml_grid_hd.flatten() if not math.isnan(x))
+            vmin_hd = min(x for x in iml_grid_hd.flatten() if not isnan(x))
+            vmax_hd = max(x for x in iml_grid_hd.flatten() if not isnan(x))
             trim_thresh = vmin
             iml_grid_hd[iml_grid_hd < trim_thresh] = np.nan