diff --git a/src/estimator/execute.jl b/src/estimator/execute.jl
index 25eff2eff..cd6cc160d 100644
--- a/src/estimator/execute.jl
+++ b/src/estimator/execute.jl
@@ -203,7 +203,7 @@ end
 (estim::StateEstimator)(d=estim.buffer.empty) = evaloutput(estim, d)
 
 @doc raw"""
-    preparestate!(estim::StateEstimator, ym, d=estim.model.dop) -> x̂
+    preparestate!(estim::StateEstimator, ym, d=[]) -> x̂
 
 Prepare `estim.x̂0` estimate with meas. outputs `ym` and dist. `d` for the current time step.
 
@@ -231,7 +231,7 @@ julia> x̂ = preparestate!(estim1, [1])
  0.0
 ```
 """
-function preparestate!(estim::StateEstimator, ym, d=estim.model.dop)
+function preparestate!(estim::StateEstimator, ym, d=estim.buffer.empty)
     if estim.direct
         validate_args(estim, ym, d)
         y0m, d0 = remove_op!(estim, ym, d)
diff --git a/src/model/nonlinmodel.jl b/src/model/nonlinmodel.jl
index 8e17691d9..671e7bd47 100644
--- a/src/model/nonlinmodel.jl
+++ b/src/model/nonlinmodel.jl
@@ -80,8 +80,8 @@ defined as ``d(t) = t``. The functions can be implemented in two possible ways:
 
 `Ts` is the sampling time in second. `nu`, `nx`, `ny` and `nd` are the respective number of 
 manipulated inputs, states, outputs and measured disturbances. The keyword argument `p`
-is the parameters of the model passed to the two functions. It can be of any Julia object 
-but use a mutable type if you want to change them later e.g.: a vector.
+is the parameters of the model passed to the two functions. It can be any Julia objects but
+use a mutable type if you want to change them later e.g.: a vector.
 
 !!! tip
     Replace the `d` or `p` argument with `_` in your functions if not needed (see Examples below).