diff --git a/book.toml b/book.toml
index 5822788..1ef6742 100644
--- a/book.toml
+++ b/book.toml
@@ -15,6 +15,7 @@ edit-url-template = "https://github.com/rust-tieng-viet/rust-tieng-viet.github.i
 [output.linkcheck]
 # Check links on the internet
 follow-web-links = false
+optional = true
 
 [output.html.playground]
 editable = true
diff --git a/dev.sh b/dev.sh
index 363b73b..cb0b197 100755
--- a/dev.sh
+++ b/dev.sh
@@ -1,8 +1,15 @@
 #!/bin/bash
 
+PORT=${1:-3000}
+
 if ! command -v mdbook &>/dev/null; then
   echo Installing mdBook https://rust-lang.github.io/mdBook/guide/installation.html ...
   cargo install mdbook
 fi
 
-mdbook serve --open
+if ! command -v mdbook-linkcheck &>/dev/null; then
+  echo Installing mdbook-linkcheck
+  cargo install mdbook-linkcheck
+fi
+
+mdbook serve --open --port $PORT