diff --git a/DESCRIPTION b/DESCRIPTION
index 7e416811..78a3ac98 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -16,7 +16,7 @@ Description: In computationally demanding analysis projects,
   'clustermq' by Schubert (2019) <doi:10.1093/bioinformatics/btz284>),
   and 'batchtools' by Lang, Bischel, and Surmann (2017)
   <doi:10.21105/joss.00135>.
-Version: 0.9.3.9000
+Version: 0.9.3.9001
 License: MIT + file LICENSE
 URL: https://wlandau.github.io/crew/, https://github.com/wlandau/crew
 BugReports: https://github.com/wlandau/crew/issues
diff --git a/NEWS.md b/NEWS.md
index c1b5a401..b5a67b1f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,6 +1,6 @@
-# crew 0.9.3.9000 (development)
-
+# crew 0.9.3.9001 (development)
 
+* Do not use extended tasks in Shiny vignette.
 
 # crew 0.9.3
 
diff --git a/vignettes/shiny.Rmd b/vignettes/shiny.Rmd
index a2c56975..a66515f9 100644
--- a/vignettes/shiny.Rmd
+++ b/vignettes/shiny.Rmd
@@ -174,12 +174,14 @@ The previous app feels choppy because it only refreshes every half second. Using
 The revised app has two changes. First, it takes `mirai` task returned by `controller$push()` and turns it into a special [`promise`](https://rstudio.github.io/promises/). This [`promise`](https://rstudio.github.io/promises/) updates the coin flip counts as soon as the flip finishes.
 
 ```r
-observeEvent(input$button, {
-  for (task in seq_len(1000)) {
+observeEvent(
+  input$button,
+  replicate(
+    1000,
     controller$push(flip_coin(), data = list(flip_coin = flip_coin)) %...>%
       collect_flips(controller, flips)
-  }
-})
+  )
+)
 ```
 
 The `collect_flips()` function collects all the finished flips and updates the flip counts.
@@ -229,12 +231,14 @@ server <- function(input, output, session) {
   flips <- reactiveValues(heads = 0, tails = 0, total = 0)
   
   # Flip a batch of coins when the button is pressed.
-  observeEvent(input$button, {
-    for (task in seq_len(1000)) {
+  observeEvent(
+    input$button,
+    replicate(
+      1000,
       controller$push(flip_coin(), data = list(flip_coin = flip_coin)) %...>%
         collect_flips(controller, flips)
-    }
-  })
+    )
+  )
 
   # Print time and flip counts.
   output$results <- renderText({