diff --git a/pyzebra/app/panel_param_study.py b/pyzebra/app/panel_param_study.py
index e73cbfe..4bb00f5 100644
--- a/pyzebra/app/panel_param_study.py
+++ b/pyzebra/app/panel_param_study.py
@@ -376,6 +376,8 @@ def create():
                 x.append(p)
                 param_fit_val = s["fit"].params[fit_param].value
                 param_fit_std = s["fit"].params[fit_param].stderr
+                if param_fit_std is None:
+                    param_fit_std = 0
                 y.append(param_fit_val)
                 y_lower.append(param_fit_val - param_fit_std)
                 y_upper.append(param_fit_val + param_fit_std)
diff --git a/pyzebra/ccl_io.py b/pyzebra/ccl_io.py
index bd053ae..6a7b048 100644
--- a/pyzebra/ccl_io.py
+++ b/pyzebra/ccl_io.py
@@ -382,7 +382,11 @@ def export_param_study(dataset, param_data, path):
 
         fit_str = ""
         for fit_param in scan["fit"].params.values():
-            fit_str = fit_str + f"{fit_param.value:<20.2f}" + f"{fit_param.stderr:<20.2f}"
+            fit_param_val = fit_param.value
+            fit_param_std = fit_param.stderr
+            if fit_param_std is None:
+                fit_param_std = 0
+            fit_str = fit_str + f"{fit_param_val:<20.2f}" + f"{fit_param_std:<20.2f}"
 
         _, fname_str = os.path.split(scan["original_filename"])