diff --git a/model_tools/parameters_storage.py b/model_tools/parameters_storage.py
index 8887d94d471a3b184f7fd9245f2a0f6da85ad1a9..20aee2aaf0e6864d7547ce2182156da96a969b69 100644
--- a/model_tools/parameters_storage.py
+++ b/model_tools/parameters_storage.py
@@ -23,7 +23,7 @@ class ParametersStorage(NestedMKDict):
 
         df.insert(4, 'sigma_rel_perc', df['sigma'])
         df['sigma_rel_perc'] = df['sigma']/df['central']*100.
-        df['sigma_rel_perc'][df['central']==0] = nan
+        df['sigma_rel_perc'].mask(df['central']==0, nan, inplace=True)
 
         for key in ('central', 'sigma', 'sigma_rel_perc'):
             if df[key].isna().all():