diff --git a/content/dev/build/android/_index.en.md b/content/dev/build/android/_index.en.md
index 5ce6b609..a6c4d496 100644
--- a/content/dev/build/android/_index.en.md
+++ b/content/dev/build/android/_index.en.md
@@ -20,6 +20,7 @@ unzip android-ndk-r22b-linux-x86_64.zip
 
 # install ffigen and llvm 
 dart pub global activate ffigen
+# on Ubuntu 18, it is: sudo apt install libclang-9-dev
 sudo apt-get install libclang-dev
 
 git clone https://github.com/rustdesk/rustdesk
diff --git a/content/dev/build/android/_index.zh-cn.md b/content/dev/build/android/_index.zh-cn.md
index 24f162a8..d68f7874 100644
--- a/content/dev/build/android/_index.zh-cn.md
+++ b/content/dev/build/android/_index.zh-cn.md
@@ -20,6 +20,7 @@ unzip android-ndk-r22b-linux-x86_64.zip
 
 # install ffigen and llvm 
 dart pub global activate ffigen
+# on Ubuntu 18, it is: sudo apt install libclang-9-dev
 sudo apt-get install libclang-dev
 
 git clone https://github.com/rustdesk/rustdesk
diff --git a/content/dev/build/android/_index.zh-tw.md b/content/dev/build/android/_index.zh-tw.md
index eb0dab87..5c632929 100644
--- a/content/dev/build/android/_index.zh-tw.md
+++ b/content/dev/build/android/_index.zh-tw.md
@@ -20,6 +20,7 @@ unzip android-ndk-r22b-linux-x86_64.zip
 
 # install ffigen and llvm 
 dart pub global activate ffigen
+# on Ubuntu 18, it is: sudo apt install libclang-9-dev
 sudo apt-get install libclang-dev
 
 git clone https://github.com/rustdesk/rustdesk