diff --git a/scripts/base_network.py b/scripts/base_network.py
index eeb87bf5d..2fa31f98c 100644
--- a/scripts/base_network.py
+++ b/scripts/base_network.py
@@ -560,7 +560,7 @@ def prefer_voltage(x, which):
         ~buses["under_construction"]
     )
 
-    c_nan_b = buses.country == "na"
+    c_nan_b = buses.country.fillna("na") == "na"
     if c_nan_b.sum() > 0:
         c_tag = _get_country(buses.loc[c_nan_b])
         c_tag.loc[~c_tag.isin(countries)] = np.nan