diff --git a/src/fix_thermal_conductivity.cpp b/src/fix_thermal_conductivity.cpp
index 8b46ff807e..5be5ed0ae4 100644
--- a/src/fix_thermal_conductivity.cpp
+++ b/src/fix_thermal_conductivity.cpp
@@ -51,7 +51,8 @@ FixThermalConductivity::FixThermalConductivity(LAMMPS *lmp,
   else error->all("Illegal fix thermal/conductivity command");
 
   nbin = atoi(arg[5]);
-  if (nbin < 3) error->all("Illegal fix thermal/conductivity command");
+  if (nbin % 2 || nbin <= 2) 
+    error->all("Illegal fix thermal/conductivity command");
 
   // optional keywords
 
@@ -105,8 +106,7 @@ void FixThermalConductivity::init()
   // set bounds of 2 slabs in edim
   // only necessary for static box, else re-computed in end_of_step()
   // lo bin is always bottom bin
-  // if nbin even, hi bin is just above half height
-  // if nbin odd, hi bin straddles half height
+  // hi bin is just above half height
 
   if (domain->box_change == 0) {
     prd = domain->prd[edim];
diff --git a/src/fix_viscosity.cpp b/src/fix_viscosity.cpp
index cd29ac85ff..39a8936fb5 100644
--- a/src/fix_viscosity.cpp
+++ b/src/fix_viscosity.cpp
@@ -56,7 +56,7 @@ FixViscosity::FixViscosity(LAMMPS *lmp, int narg, char **arg) :
   else error->all("Illegal fix viscosity command");
 
   nbin = atoi(arg[6]);
-  if (nbin < 3) error->all("Illegal fix viscosity command");
+  if (nbin % 2 || nbin <= 2) error->all("Illegal fix viscosity command");
 
   // optional keywords
 
@@ -116,8 +116,7 @@ void FixViscosity::init()
   // set bounds of 2 slabs in pdim
   // only necessary for static box, else re-computed in end_of_step()
   // lo bin is always bottom bin
-  // if nbin even, hi bin is just above half height
-  // if nbin odd, hi bin straddles half height
+  // hi bin is just above half height
 
   if (domain->box_change == 0) {
     prd = domain->prd[pdim];