diff --git a/src/rmn.cpp b/src/rmn.cpp
index cd266a4..5f9649f 100644
--- a/src/rmn.cpp
+++ b/src/rmn.cpp
@@ -43,8 +43,8 @@ void estimateZ(
   double& lnL
 ){
   arma::uword L = z.size();
-  std::vector<double> F(L + 1);
-  std::vector<double> B(L + 1);
+  std::vector<double> F(L + 2);
+  std::vector<double> B(L + 2);
   std::vector<double>::iterator F_it = F.begin();
   std::vector<double>::reverse_iterator B_it = B.rbegin();
   std::vector<double>::const_iterator forlnEmPN_it = lnEmPN.begin();
@@ -73,7 +73,7 @@ void estimateZ(
 
   // calculate posterior;
   forlnEmPN_it = lnEmPN.begin();
-  for (i = 0; i < L; i++){
+  for (i = 1; i <= L; i++){
     empty(i - 1) = exp(F[i - 1] + B[i + 1] - lnL);
 
     if (i >= w){