diff --git a/R/parallel.R b/R/parallel.R
index 9c835b06..5f81d2e1 100644
--- a/R/parallel.R
+++ b/R/parallel.R
@@ -22,8 +22,8 @@
 #' `"mc.cores"` option:
 #' 
 #' ```r
-#' options(mc.cores = parallel::detectCores())  # use all available cores
-#' options(mc.cores = 4L)                        # or a fixed number
+#' options(mc.cores = parallelly::availableCores())  # use all available cores
+#' options(mc.cores = 4L)                             # or a fixed number
 #' ```
 #' 
 #' The default is `1` (single-threaded).
diff --git a/R/tree_distance_info.R b/R/tree_distance_info.R
index 3cfe8c69..a6ad95d4 100644
--- a/R/tree_distance_info.R
+++ b/R/tree_distance_info.R
@@ -128,8 +128,8 @@
 #' automatically.  Control the number of threads with the `"mc.cores"` option:
 #' 
 #' ```r
-#' options(mc.cores = parallel::detectCores())  # use all cores
-#' options(mc.cores = 4L)                        # or a fixed number
+#' options(mc.cores = parallelly::availableCores())  # use all cores
+#' options(mc.cores = 4L)                             # or a fixed number
 #' ```
 #' 
 #' Do **not** call [`StartParallel()`] for these functions: a registered
diff --git a/man/StartParallel.Rd b/man/StartParallel.Rd
index 1a918897..0cbf7a10 100644
--- a/man/StartParallel.Rd
+++ b/man/StartParallel.Rd
@@ -54,8 +54,8 @@ no cluster setup is required.  The affected functions are:
 The number of \acronym{OpenMP} threads is controlled by the standard
 \code{"mc.cores"} option:
 
-\if{html}{\out{<div class="sourceCode r">}}\preformatted{options(mc.cores = parallel::detectCores())  # use all available cores
-options(mc.cores = 4L)                        # or a fixed number
+\if{html}{\out{<div class="sourceCode r">}}\preformatted{options(mc.cores = parallelly::availableCores())  # use all available cores
+options(mc.cores = 4L)                             # or a fixed number
 }\if{html}{\out{</div>}}
 
 The default is \code{1} (single-threaded).
diff --git a/man/TreeDistance.Rd b/man/TreeDistance.Rd
index f753909c..dd0fdce5 100644
--- a/man/TreeDistance.Rd
+++ b/man/TreeDistance.Rd
@@ -263,8 +263,8 @@ When \code{tree2 = NULL} and all trees share the same tip labels, pairwise
 distance calculation uses a multi-threaded \acronym{OpenMP} batch path
 automatically.  Control the number of threads with the \code{"mc.cores"} option:
 
-\if{html}{\out{<div class="sourceCode r">}}\preformatted{options(mc.cores = parallel::detectCores())  # use all cores
-options(mc.cores = 4L)                        # or a fixed number
+\if{html}{\out{<div class="sourceCode r">}}\preformatted{options(mc.cores = parallelly::availableCores())  # use all cores
+options(mc.cores = 4L)                             # or a fixed number
 }\if{html}{\out{</div>}}
 
 Do \strong{not} call \code{\link[=StartParallel]{StartParallel()}} for these functions: a registered