diff --git a/src/model/formulations/base/system.jl b/src/model/formulations/base/system.jl
index c11c1bb..01c9a9b 100644
--- a/src/model/formulations/base/system.jl
+++ b/src/model/formulations/base/system.jl
@@ -84,7 +84,7 @@ function _add_reserve_eqs!(model::JuMP.Model)::Nothing
         # Account for shortfall contribution to objective
         if shortfall_penalty > 1e-7
             add_to_expression!(
-                model.obj,
+                model[:obj],
                 shortfall_penalty,
                 model[:reserve_shortfall][t],
             )