diff --git a/src/seismic_hazard_forecasting.py b/src/seismic_hazard_forecasting.py
index f4e66c7..24880b5 100644
--- a/src/seismic_hazard_forecasting.py
+++ b/src/seismic_hazard_forecasting.py
@@ -81,6 +81,7 @@ def main(catalog_file, mc_file, pdf_file, m_file, m_select, mag_label, mc, m_max
         m_range = [None]
     else:
         m_range = read_mat_m(m_file)
+        m_max = m_range[-1] # take m_max from the m_file
 
     if verbose:
         logger.setLevel(logging.DEBUG)
@@ -320,8 +321,8 @@ verbose: {verbose}")
     lambdas = [None]
     if custom_rate != None and forecast_select:
         logger.info(f"Using activity rate specified by user: {custom_rate} per {time_unit}")
-        lambdas = [custom_rate]
-        lambdas_perc = [1]
+        lambdas = np.array([custom_rate], dtype='d')
+        lambdas_perc = np.array([1], dtype='d')
 
     elif rate_select:
         logger.info(f"Activity rate modeling selected")
@@ -377,8 +378,11 @@ verbose: {verbose}")
 
         # validate m_max against the grond motion model
         models_anthro_limited = ['Lasocki2013', 'Atkinson2015', 'ConvertitoEtAl2012Geysers'] # these models require that m_max<=4.5
-        if m_max > 4.5 and model in models_anthro_limited: 
-            msg = f"Selected ground motion model {model} is only valid up to a maximum magnitude of 4.5. Please try again with a lower maximum magnitude."
+        if m_max > 4.5 and model in models_anthro_limited:
+            if m_file is None: 
+                msg = f"The selected ground motion model {model} is only valid for magnitudes up to 4.5. Please select a lower maximum magnitude."
+            else:
+                msg = f"The selected ground motion model {model} is only valid for magnitudes up to 4.5, but the provided magnitude file includes values up to {m_max}. Please adjust the magnitude range in the file accordingly."
             logger.error(msg)
             raise Exception(msg)
 
@@ -462,7 +466,7 @@ verbose: {verbose}")
                 imls = [dask.delayed(compute_IMT_exceedance)(rx_lat[i], rx_lon[i], distances[i].flatten(), fr, p, lambdas,
                                                             forecast_len, lambdas_perc, m_range, m_pdf, m_cdf, model,
                                                             log_level=logging.DEBUG, imt=imt, IMT_min=0.0, IMT_max=2.0, rx_label=i,
-                                                            rtol=0.1, use_cython=False) for i in iter]
+                                                            rtol=0.1, use_cython=True) for i in iter]
                 iml = dask.compute(*imls)
                 iml_grid_raw.append(list(iml))
 
@@ -474,7 +478,7 @@ verbose: {verbose}")
                 for i in iter:
                     iml_i = compute_IMT_exceedance(rx_lat[i], rx_lon[i], distances[i].flatten(), fr, p, lambdas, forecast_len, 
                                                     lambdas_perc, m_range, m_pdf, m_cdf, model, imt=imt, IMT_min = 0.0,
-                                                    IMT_max = 2.0, rx_label = i, rtol = 0.1, use_cython=False)
+                                                    IMT_max = 2.0, rx_label = i, rtol = 0.1, use_cython=True)
                     iml.append(iml_i)
                     logger.info(f"Estimated {imt} at rx {i} is {iml_i}")
                 iml_grid_raw.append(iml)