diff --git a/CHANGELOG.md b/CHANGELOG.md
index 610248f02..d787c8bee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Main (unreleased)
 
+- Warn when relying on default Node.js or Yarn versions (https://github.com/heroku/heroku-buildpack-ruby/pull/1401)
+- Warn when default Node.js or Yarn versions change (https://github.com/heroku/heroku-buildpack-ruby/pull/1401)
+
 ## v261 (2023/11/02)
 
 - JRuby 9.4.5.0 is now available
diff --git a/lib/language_pack/helpers/nodebin.rb b/lib/language_pack/helpers/nodebin.rb
index 0bffcd3aa..1a5c194f9 100644
--- a/lib/language_pack/helpers/nodebin.rb
+++ b/lib/language_pack/helpers/nodebin.rb
@@ -1,19 +1,20 @@
 require 'json'
 
 class LanguagePack::Helpers::Nodebin
+  NODE_VERSION = "20.9.0"
+  YARN_VERSION = "1.22.19"
+
   def self.hardcoded_node_lts
-    version = "20.9.0"
     {
-      "number" => version,
-      "url"    => "https://heroku-nodebin.s3.us-east-1.amazonaws.com/node/release/linux-x64/node-v#{version}-linux-x64.tar.gz"
+      "number" => NODE_VERSION,
+      "url"    => "https://heroku-nodebin.s3.us-east-1.amazonaws.com/node/release/linux-x64/node-v#{NODE_VERSION}-linux-x64.tar.gz"
     }
   end
 
   def self.hardcoded_yarn
-    version = "1.22.19"
     {
-      "number" => version,
-      "url"    => "https://heroku-nodebin.s3.us-east-1.amazonaws.com/yarn/release/yarn-v#{version}.tar.gz"
+      "number" => YARN_VERSION,
+      "url"    => "https://heroku-nodebin.s3.us-east-1.amazonaws.com/yarn/release/yarn-v#{YARN_VERSION}.tar.gz"
     }
   end
 
diff --git a/lib/language_pack/ruby.rb b/lib/language_pack/ruby.rb
index 81784e273..beb1b0f0d 100644
--- a/lib/language_pack/ruby.rb
+++ b/lib/language_pack/ruby.rb
@@ -1018,6 +1018,26 @@ def add_node_js_binary
     if Pathname(build_path).join("package.json").exist? ||
          bundler.has_gem?('execjs') ||
          bundler.has_gem?('webpacker')
+
+      version = @node_installer.version
+      old_version = @metadata.fetch("default_node_version") { version }
+
+      if version != version
+        warn(<<~WARNING, inline: true)
+          Default version of Node.js changed (#{old_version} to #{version})
+        WARNING
+      end
+
+      warn(<<~WARNING, inline: true)
+        Installing a default version (#{version}) of Node.js.
+        This version is not pinned and can change over time, causing unexpected failures.
+
+        Heroku recommends placing the `heroku/nodejs` buildpack in front of
+        `heroku/ruby` to install a specific version of node:
+
+        https://devcenter.heroku.com/articles/ruby-support#node-js-support
+      WARNING
+
       [@node_installer.binary_path]
     else
       []
@@ -1028,6 +1048,26 @@ def add_yarn_binary
     return [] if yarn_preinstalled?
 
     if Pathname(build_path).join("yarn.lock").exist? || bundler.has_gem?('webpacker')
+
+      version = @yarn_installer.version
+      old_version = @metadata.fetch("default_yarn_version") { version }
+
+      if version != version
+        warn(<<~WARNING, inline: true)
+          Default version of Yarn changed (#{old_version} to #{version})
+        WARNING
+      end
+
+      warn(<<~WARNING, inline: true)
+        Installing a default version (#{version}) of Yarn
+        This version is not pinned and can change over time, causing unexpected failures.
+
+        Heroku recommends placing the `heroku/nodejs` buildpack in front of
+        `heroku/ruby` to install a specific version of node:
+
+        https://devcenter.heroku.com/articles/ruby-support#node-js-support
+      WARNING
+
       [@yarn_installer.name]
     else
       []
diff --git a/spec/hatchet/node_spec.rb b/spec/hatchet/node_spec.rb
index 7d58b22d2..fe816dc27 100644
--- a/spec/hatchet/node_spec.rb
+++ b/spec/hatchet/node_spec.rb
@@ -16,6 +16,9 @@
       expect(app.output).to include("bin/node is the node directory")
       expect(app.output).to_not include(".heroku/node/bin/node is the node directory")
 
+      expect(app.output).to include("Installing a default version (#{LanguagePack::Helpers::Nodebin::YARN_VERSION}) of Yarn")
+      expect(app.output).to include("Installing a default version (#{LanguagePack::Helpers::Nodebin::NODE_VERSION}) of Node.js")
+
       expect(app.run("which node")).to match("/app/bin/node")     # We put node in bin/node
       expect(app.run("which yarn")).to match("/app/vendor/yarn-") # We put yarn in /app/vendor/yarn-
     end