diff --git a/Examples/PerfectFluid/Fluxes.hpp b/Examples/PerfectFluid/Fluxes.hpp
index acb26d5c7..e7080af9e 100644
--- a/Examples/PerfectFluid/Fluxes.hpp
+++ b/Examples/PerfectFluid/Fluxes.hpp
@@ -56,12 +56,12 @@ vars_t<data_t> compute_flux(const vars_t<data_t> &vars, const int idir)
 }
 template <class data_t, template <typename> class vars_t>
 vars_t<data_t> compute_num_flux(const vars_t<data_t> &vars, const int idir,
-                                const double lambda)
+                                const double lambda, const int sign)
 {
     vars_t<data_t> out = compute_flux(vars, idir);
-    out.D -= lambda * vars.D;
-    FOR(j) out.Sj[j] -= lambda * vars.Sj[j];
-    out.tau -= lambda * vars.tau;
+    out.D += sign * lambda * vars.D;
+    FOR(j) out.Sj[j] += sign * lambda * vars.Sj[j];
+    out.tau += sign * lambda * vars.tau;
     return out;
 }
 
diff --git a/Examples/PerfectFluid/PerfectFluid.impl.hpp b/Examples/PerfectFluid/PerfectFluid.impl.hpp
index 3e693e727..a7c9ef6b1 100644
--- a/Examples/PerfectFluid/PerfectFluid.impl.hpp
+++ b/Examples/PerfectFluid/PerfectFluid.impl.hpp
@@ -110,7 +110,7 @@ void PerfectFluid<eos_t>::add_matter_rhs(
         FOR(j) { vars_right_p.vi[j] = rp.vi[j][idir]; }
         ConservativeRecovery::PtoC(vars_right_p);
         vars_t<data_t> flux_right_p =
-            Fluxes::compute_num_flux(vars_right_p, idir, m_lambda);
+            Fluxes::compute_num_flux(vars_right_p, idir, m_lambda, -1);
 
         vars_t<data_t> vars_right_m = vars;
         vars_right_m.rho = rm.rho[idir];
@@ -118,7 +118,7 @@ void PerfectFluid<eos_t>::add_matter_rhs(
         FOR(j) vars_right_m.vi[j] = rm.vi[j][idir];
         ConservativeRecovery::PtoC(vars_right_m);
         vars_t<data_t> flux_right_m =
-            Fluxes::compute_num_flux(vars_right_m, idir, m_lambda);
+            Fluxes::compute_num_flux(vars_right_m, idir, m_lambda, 1);
 
         rhs.D += -1. / (2. * m_dx) * (flux_right_p.D + flux_right_m.D);
         FOR(j)
@@ -137,7 +137,7 @@ void PerfectFluid<eos_t>::add_matter_rhs(
         FOR(j) { vars_left_p.vi[j] = lp.vi[j][idir]; }
         ConservativeRecovery::PtoC(vars_left_p);
         vars_t<data_t> flux_left_p =
-            Fluxes::compute_num_flux(vars_left_p, idir, m_lambda);
+            Fluxes::compute_num_flux(vars_left_p, idir, m_lambda, -1);
 
         vars_t<data_t> vars_left_m = vars;
         vars_left_m.rho = lm.rho[idir];
@@ -145,7 +145,7 @@ void PerfectFluid<eos_t>::add_matter_rhs(
         FOR(j) { vars_left_m.vi[j] = lm.vi[j][idir]; }
         ConservativeRecovery::PtoC(vars_left_m);
         vars_t<data_t> flux_left_m =
-            Fluxes::compute_num_flux(vars_left_m, idir, m_lambda);
+            Fluxes::compute_num_flux(vars_left_m, idir, m_lambda, 1);
 
         rhs.D += 1. / (2. * m_dx) * (flux_left_p.D + flux_left_m.D);
         FOR(j)