diff --git a/src/HydroBlast2D/test_hydro2d_blast.cpp b/src/HydroBlast2D/test_hydro2d_blast.cpp
index f16efbea7..f159f7b55 100644
--- a/src/HydroBlast2D/test_hydro2d_blast.cpp
+++ b/src/HydroBlast2D/test_hydro2d_blast.cpp
@@ -27,7 +27,7 @@ struct BlastProblem {
 
 template <> struct quokka::EOS_Traits<BlastProblem> {
 	static constexpr double gamma = 5. / 3.;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroBlast3D/test_hydro3d_blast.cpp b/src/HydroBlast3D/test_hydro3d_blast.cpp
index c4e660b90..d5ef9efe5 100644
--- a/src/HydroBlast3D/test_hydro3d_blast.cpp
+++ b/src/HydroBlast3D/test_hydro3d_blast.cpp
@@ -34,7 +34,7 @@ bool test_passes = false; // if one of the energy checks fails, set to false
 
 template <> struct quokka::EOS_Traits<SedovProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroHighMach/test_hydro_highmach.cpp b/src/HydroHighMach/test_hydro_highmach.cpp
index 68e50c54d..e52487813 100644
--- a/src/HydroHighMach/test_hydro_highmach.cpp
+++ b/src/HydroHighMach/test_hydro_highmach.cpp
@@ -30,7 +30,7 @@ struct HighMachProblem {
 
 template <> struct quokka::EOS_Traits<HighMachProblem> {
 	static constexpr double gamma = 5. / 3.;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp b/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp
index 3cb6373e1..6df2ebb41 100644
--- a/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp
+++ b/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp
@@ -24,7 +24,7 @@ struct KelvinHelmholzProblem {
 
 template <> struct quokka::EOS_Traits<KelvinHelmholzProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroQuirk/test_quirk.cpp b/src/HydroQuirk/test_quirk.cpp
index fed2691d8..983e65a79 100644
--- a/src/HydroQuirk/test_quirk.cpp
+++ b/src/HydroQuirk/test_quirk.cpp
@@ -43,7 +43,7 @@ struct QuirkProblem {
 
 template <> struct quokka::EOS_Traits<QuirkProblem> {
 	static constexpr double gamma = 5. / 3.;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroRichtmeyerMeshkov/test_hydro2d_rm.cpp b/src/HydroRichtmeyerMeshkov/test_hydro2d_rm.cpp
index b36dbb67c..718589507 100644
--- a/src/HydroRichtmeyerMeshkov/test_hydro2d_rm.cpp
+++ b/src/HydroRichtmeyerMeshkov/test_hydro2d_rm.cpp
@@ -23,7 +23,7 @@ struct RichtmeyerMeshkovProblem {
 
 template <> struct quokka::EOS_Traits<RichtmeyerMeshkovProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroShocktube/test_hydro_shocktube.cpp b/src/HydroShocktube/test_hydro_shocktube.cpp
index 423d55908..ebf3cce8e 100644
--- a/src/HydroShocktube/test_hydro_shocktube.cpp
+++ b/src/HydroShocktube/test_hydro_shocktube.cpp
@@ -28,7 +28,7 @@ struct ShocktubeProblem {
 
 template <> struct quokka::EOS_Traits<ShocktubeProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroShocktubeCMA/test_hydro_shocktube_cma.cpp b/src/HydroShocktubeCMA/test_hydro_shocktube_cma.cpp
index e608e56dc..02f471cd8 100644
--- a/src/HydroShocktubeCMA/test_hydro_shocktube_cma.cpp
+++ b/src/HydroShocktubeCMA/test_hydro_shocktube_cma.cpp
@@ -33,7 +33,7 @@ template <> struct SimulationData<ShocktubeProblem> {
 
 template <> struct quokka::EOS_Traits<ShocktubeProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/HydroVacuum/test_hydro_vacuum.cpp b/src/HydroVacuum/test_hydro_vacuum.cpp
index 11cfce308..217b43e1c 100644
--- a/src/HydroVacuum/test_hydro_vacuum.cpp
+++ b/src/HydroVacuum/test_hydro_vacuum.cpp
@@ -27,7 +27,7 @@ struct ShocktubeProblem {
 
 template <> struct quokka::EOS_Traits<ShocktubeProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/RayleighTaylor2D/test_hydro2d_rt.cpp b/src/RayleighTaylor2D/test_hydro2d_rt.cpp
index fb2912277..645ba6311 100644
--- a/src/RayleighTaylor2D/test_hydro2d_rt.cpp
+++ b/src/RayleighTaylor2D/test_hydro2d_rt.cpp
@@ -24,7 +24,7 @@ struct RTProblem {
 
 template <> struct quokka::EOS_Traits<RTProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/SphericalCollapse/spherical_collapse.cpp b/src/SphericalCollapse/spherical_collapse.cpp
index 7a0a420a2..1aeaf6967 100644
--- a/src/SphericalCollapse/spherical_collapse.cpp
+++ b/src/SphericalCollapse/spherical_collapse.cpp
@@ -28,7 +28,7 @@ struct CollapseProblem {
 
 template <> struct quokka::EOS_Traits<CollapseProblem> {
 	static constexpr double gamma = 5. / 3.;
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
diff --git a/src/StarCluster/star_cluster.cpp b/src/StarCluster/star_cluster.cpp
index c7911df76..832593c2b 100644
--- a/src/StarCluster/star_cluster.cpp
+++ b/src/StarCluster/star_cluster.cpp
@@ -37,7 +37,7 @@ struct StarCluster {
 template <> struct quokka::EOS_Traits<StarCluster> {
 	static constexpr double gamma = 1.0;
 	static constexpr double cs_isothermal = 1.0; // dimensionless
-	static constexpr double mean_molecular_weight = 1.0;
+	static constexpr double mean_molecular_weight = C::m_u;
 	static constexpr double boltzmann_constant = C::k_B;
 };