diff --git a/optlang/gurobi_interface.py b/optlang/gurobi_interface.py
index 9d5ddff5..23ee0629 100644
--- a/optlang/gurobi_interface.py
+++ b/optlang/gurobi_interface.py
@@ -238,7 +238,8 @@ def problem(self, value):
     @property
     def primal(self):
         if self.problem is not None:
-            return self._internal_constraint.Slack
+            return (self._internal_constraint.RHS -
+                    self._internal_constraint.Slack)
             # return self._round_primal_to_bounds(primal_from_solver)  # Test assertions fail
             # return primal_from_solver
         else: