diff --git a/planning/planners/src/encode.rs b/planning/planners/src/encode.rs
index 0dea2b26..f3a4f581 100644
--- a/planning/planners/src/encode.rs
+++ b/planning/planners/src/encode.rs
@@ -456,8 +456,9 @@ pub fn add_metric(pb: &FiniteProblem, model: &mut Model, metric: Metric) -> IAto
         Metric::MaximizeVar(to_maximize) => {
             // we must return a variable to minimize.
             // return a new variable constrained to be the negation of the one to maximize
+            // to_maximize = -to_minimize
             let to_minimize = model.new_ivar(INT_CST_MIN, INT_CST_MAX, VarLabel(Container::Base, VarType::Cost));
-            let sum = LinearSum::zero() + to_maximize - to_minimize;
+            let sum = LinearSum::zero() + to_maximize + to_minimize;
             model.enforce(sum.clone().leq(0), []);
             model.enforce(sum.geq(0), []);
             to_minimize.into()
diff --git a/solver/src/model/lang/linear.rs b/solver/src/model/lang/linear.rs
index 7f930bb6..61a30bf8 100644
--- a/solver/src/model/lang/linear.rs
+++ b/solver/src/model/lang/linear.rs
@@ -426,6 +426,12 @@ impl std::fmt::Display for LinearLeq {
     }
 }
 
+impl std::fmt::Debug for LinearLeq {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{self}")
+    }
+}
+
 impl LinearLeq {
     pub fn new(sum: LinearSum, ub: IntCst) -> LinearLeq {
         LinearLeq { sum, ub }