diff --git a/src/arx.jl b/src/arx.jl
index d074eafd70a2e03c5735dfd2af81445e09b66a94..faa71a9d2f0c4be0b32f1e196244776246d40cbc 100644
--- a/src/arx.jl
+++ b/src/arx.jl
@@ -52,7 +52,7 @@ function getARXregressor(y::AbstractVector,u::AbstractVecOrMat, na, nb)
     y    = copy(A[:,1])
     A    = A[:,2:end]
     for i = 1:length(nb)
-        offs = m-nb[i]
+        offs = m-nb[i]-1
         A = [A toeplitz(u[nb[i]+offs:n+nb[i]+offs-1,i],u[nb[i]+offs:-1:1+offs,i])]
     end
     return y,A