diff --git a/message_ix_models/data/emission.yaml b/message_ix_models/data/emission.yaml
index 481da3c21e..4318f130d5 100644
--- a/message_ix_models/data/emission.yaml
+++ b/message_ix_models/data/emission.yaml
@@ -13,6 +13,7 @@ CO2:
 
 N2O:
   name: Nitrous oxide
+  units: kt
 
 NH3:
   name: Ammonia