diff --git a/samples/matlab/reactor1.m b/samples/matlab/reactor1.m
index 9a9e989a1..a15af66c6 100644
--- a/samples/matlab/reactor1.m
+++ b/samples/matlab/reactor1.m
@@ -20,14 +20,16 @@ end
 
 nsp = nSpecies(gas);
 
+P = oneatm
 % set the initial conditions
-set(gas,'T',1001.0,'P',oneatm,'X','H2:2,O2:1,N2:4');
+set(gas,'T',1001.0,'P',P,'X','H2:2,O2:1,N2:4');
 
 % create a reactor, and insert the gas
 r = Reactor(gas);
 
 % create a reservoir to represent the environment
 a = IdealGasMix('air.cti');
+set(a,'P',P)
 env = Reservoir(a);
 
 % Define a wall between the reactor and the environment and