diff --git a/templates/macros.html b/templates/macros.html
index 0ad625d..d51ae9b 100644
--- a/templates/macros.html
+++ b/templates/macros.html
@@ -497,7 +497,7 @@ https://www.flightradar24.com/data/flights/{{ flight.airline_detail.iata | lower
                   <span class="text-nowrap"><strong>duration:</strong> {{ flight.duration }}</span>
                 {% endif %}
                 {# <pre>{{ flight | pprint }}</pre> #}
-                {% if flight.co2_kg is not none %}
+                {% if flight.co2_kg is defined and flight.co2_kg is not none %}
                 <span class="text-nowrap"><strong>CO₂:</strong> {{ "{:,.1f}".format(flight.co2_kg) }} kg</span>
                 {% endif %}
               {% endif %}