diff --git a/tests/ep/ar.mod b/tests/ep/ar.mod
index a94a04d82..a5456efc1 100644
--- a/tests/ep/ar.mod
+++ b/tests/ep/ar.mod
@@ -2,7 +2,7 @@ var Efficiency, efficiency;
 
 varexo EfficiencyInnovation;
 
-parameters rho, effstar, sigma2;
+parameters rho, effstar, sigma;
 
 /*
 ** Calibration
@@ -11,22 +11,22 @@ parameters rho, effstar, sigma2;
 
 rho     =  0.950;
 effstar =  1.000;
-sigma2  =  0.0001;
+sigma   =  0.0001;
 
-external_function(name=mean_preserving_spread);
+external_function(name=mean_preserving_spread,nargs=2);
 
 model;
 
   // Eq. n°1:
-  efficiency = rho*efficiency(-1) + EfficiencyInnovation;
+  efficiency = rho*efficiency(-1) + sigma*EfficiencyInnovation;
 
   // Eq. n°2:
-  Efficiency = effstar*exp(efficiency-mean_preserving_spread(rho));
+  Efficiency = effstar*exp(efficiency-mean_preserving_spread(rho,sigma));
 
 end;
 
 shocks;
-var EfficiencyInnovation = sigma2;
+var EfficiencyInnovation = 1;
 end;
 
 steady;
@@ -36,15 +36,15 @@ options_.ep.stochastic.order = 0;
 options_.ep.stochastic.nodes = 0;
 options_.console_mode = 0;
 
-ts = extended_path([],100);
+ts = extended_path([],10000);
 
 options_.ep.verbosity = 0;
 options_.ep.stochastic.order = 1;
 options_.ep.stochastic.nodes = 3;
 options_.console_mode = 0;
 
-sts = extended_path([],100);
+sts = extended_path([],10000);
 
-if max(max(abs(ts-sts)))>options_.dynatol.x
+if max(max(abs(ts-sts)))>pi*options_.dynatol.x
    disp('Stochastic Extended Path:: Something is wrong here (potential bug in extended_path.m)!!!')
-end
\ No newline at end of file
+end
diff --git a/tests/ep/mean_preserving_spread.m b/tests/ep/mean_preserving_spread.m
index d296ec345..d9d2fe45f 100644
--- a/tests/ep/mean_preserving_spread.m
+++ b/tests/ep/mean_preserving_spread.m
@@ -14,4 +14,4 @@ function m = mean_preserving_spread(autoregressive_parameter,sigma)
 %  stephane DOT adjemian AT univ DASH lemans DOT fr
 %  frederic DOT karame AT univ DASH evry DOT fr
 
-m = sigma/(1-autoregressive_parameter*autoregressive_parameter);
\ No newline at end of file
+m = .5*sigma*sigma/(1-autoregressive_parameter*autoregressive_parameter);
\ No newline at end of file