diff --git a/core/trajectory.jl b/core/trajectory.jl
index 371241530a42c23e10ec6a8277a465ecab0e3e88..8ca9ccbd8c6bc6f2210faed7bf012729ca83f525 100644
--- a/core/trajectory.jl
+++ b/core/trajectory.jl
@@ -321,7 +321,7 @@ function trajectory_from_csv(csv_file, model::ContinuousTimeModel)
         elseif model_var == "transitions"
             transitions = csv_mat_values[:,i]
         else
-            @assert Symbol(model_var) in model.g "Variable is not observed in the model"
+            @assert Symbol(model_var) in model.g "Variable $(model_var) is not observed in the model"
             values[model._map_obs_var_idx[Symbol(model_var)]] = csv_mat_values[:,i]
         end
     end