diff --git a/R/CallbackSetUnfreeze.R b/R/CallbackSetUnfreeze.R
index 87e92682..e095f944 100644
--- a/R/CallbackSetUnfreeze.R
+++ b/R/CallbackSetUnfreeze.R
@@ -3,10 +3,7 @@
 #' @name mlr_callback_set.unfreeze
 #'
 #' @description
-#' Unfreeze some weights after some number of steps or epochs. Select either a given module or a parameter.
-#'
-#' @details
-#' TODO: add
+#' Unfreeze some weights (parameters of the network) after some number of steps or epochs.
 #'
 #' @param starting_weights (`Select`)\cr
 #'  A `Select` denoting the weights that are trainable from the start.
@@ -30,8 +27,10 @@ CallbackSetUnfreeze = R6Class("CallbackSetUnfreeze",
     #' @description
     #' Sets the starting weights
     on_begin = function() {
-      weights = select_invert(self$starting_weights)(names(self$ctx$network$parameters))
-      walk(self$ctx$network$parameters[weights], function(param) param$requires_grad_(FALSE))
+      trainable_weights = self$starting_weights(names(self$ctx$network$parameters))
+      walk(self$ctx$network$parameters[trainable_weights], function(param) param$requires_grad_(TRUE))
+      frozen_weights = select_invert(self$starting_weights)(names(self$ctx$network$parameters))
+      walk(self$ctx$network$parameters[frozen_weights], function(param) param$requires_grad_(FALSE))
     },
     #' @description
     #' Unfreezes weights if the training is at the correct epoch
@@ -54,8 +53,7 @@ CallbackSetUnfreeze = R6Class("CallbackSetUnfreeze",
         }
       }
     }
-  ),
-  private = list()
+  )
 )
 
 #' @include TorchCallback.R
diff --git a/R/Select.R b/R/Select.R
index 9a167a53..766d196a 100644
--- a/R/Select.R
+++ b/R/Select.R
@@ -3,9 +3,7 @@
 #' @name Select
 #' 
 #' @description
-#' A [`Select`] function is used by the callback `CallbackSetUnfreeze` to determine a subset of parameters to freeze or unfreeze during training.
-#' 
-#' @section Details:
+#' A [`Select`] function subsets a character vector. They are used by the callback `CallbackSetUnfreeze` to select parameters to freeze or unfreeze during training.
 #' ...
 NULL
 
@@ -49,7 +47,7 @@ select_grep = function(pattern, ignore.case = FALSE, perl = FALSE, fixed = FALSE
 
 #' @describeIn Select `select_name` selects parameters with names matching the given names
 #' @export
-select_name = function(param_names, assert_present = FALSE) {
+select_name = function(param_names, assert_present = TRUE) {
   assert_character(param_names, any.missing = FALSE)
   assert_flag(assert_present)
   str_assert_present = if (assert_present) ", assert_present = TRUE" else ""
diff --git a/tests/testthat/test_Select.R b/tests/testthat/test_Select.R
index 3f353daa..f5145e80 100644
--- a/tests/testthat/test_Select.R
+++ b/tests/testthat/test_Select.R
@@ -1,14 +1,5 @@
 test_that("selectors work", {
-  n_epochs = 1
-
-  task = tsk("iris")
-
-  mlp = lrn("classif.mlp",
-            epochs = 10, batch_size = 150, neurons = c(100, 200, 300)
-  )
-  mlp$train(task)
-
-  all_params = names(mlp$network$parameters)
+  all_params = c("0.weight", "0.bias", "3.weight", "3.bias", "6.weight", "6.bias", "9.weight", "9.bias")
 
   expect_equal(selectorparam_none()(all_params), character(0))
   expect_equal(selectorparam_all()(all_params), all_params)