diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1340ab1cba..a0b72be953 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add check when capital recovery period is zero and investment costs are 
   non-zero in multi-stage GenX (#666)
 - Fix write_status with UCommit = WriteShadowPrices = 1 (#645)
+- Fix write_multi_stage_cost.jl: add discount with OPEX multipliers to 
+  cUnmetPolicyPenalty (#679)
 
 ## [0.3.7] - 2024-04-02
 
diff --git a/src/multi_stage/write_multi_stage_costs.jl b/src/multi_stage/write_multi_stage_costs.jl
index 7437628440..326a7c5fda 100644
--- a/src/multi_stage/write_multi_stage_costs.jl
+++ b/src/multi_stage/write_multi_stage_costs.jl
@@ -37,7 +37,7 @@ function write_multi_stage_costs(outpath::String, settings_d::Dict, inputs_dict:
     end
 
     # For OPEX costs, apply additional discounting
-    for cost in ["cVar", "cNSE", "cStart", "cUnmetRsv"]
+    for cost in ["cVar", "cNSE", "cStart", "cUnmetRsv", "cUnmetPolicyPenalty"]
         if cost in df_costs[!, :Costs]
             df_costs[df_costs[!, :Costs].==cost, 2:end] = transpose(OPEXMULTS) .* df_costs[df_costs[!, :Costs].==cost, 2:end]
         end