diff --git a/macos.md b/macos.md
index 80f9beb7..96818b0b 100644
--- a/macos.md
+++ b/macos.md
@@ -429,7 +429,7 @@ exec zsh
 Then run:
 
 ```bash
-brew install rbenv
+brew install rbenv libyaml
 ```
 
 
diff --git a/ubuntu.md b/ubuntu.md
index 21eed5ab..1303e487 100644
--- a/ubuntu.md
+++ b/ubuntu.md
@@ -391,7 +391,7 @@ rm -rf ~/.rbenv
 Then in the terminal, run:
 
 ```bash
-sudo apt install -y build-essential tklib zlib1g-dev libssl-dev libffi-dev libxml2 libxml2-dev libxslt1-dev libreadline-dev
+sudo apt install -y build-essential tklib zlib1g-dev libssl-dev libffi-dev libxml2 libxml2-dev libxslt1-dev libreadline-dev libyaml-dev
 ```
 
 ```bash
diff --git a/windows.md b/windows.md
index bb77befe..06fb76fa 100644
--- a/windows.md
+++ b/windows.md
@@ -929,7 +929,7 @@ rm -rf ~/.rbenv
 Then in the terminal, run:
 
 ```bash
-sudo apt install -y build-essential tklib zlib1g-dev libssl-dev libffi-dev libxml2 libxml2-dev libxslt1-dev libreadline-dev
+sudo apt install -y build-essential tklib zlib1g-dev libssl-dev libffi-dev libxml2 libxml2-dev libxslt1-dev libreadline-dev libyaml-dev
 ```
 
 ```bash