diff --git a/buildpacks/ruby/src/layers/bundle_download_layer.rs b/buildpacks/ruby/src/layers/bundle_download_layer.rs
index 066a83a8..1dedcb90 100644
--- a/buildpacks/ruby/src/layers/bundle_download_layer.rs
+++ b/buildpacks/ruby/src/layers/bundle_download_layer.rs
@@ -59,6 +59,7 @@ try_migrate_deserializer_chain!(
 );
 
 #[derive(Deserialize, Serialize, Debug, Clone, CacheDiff)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct MetadataV1 {
     #[cache_diff(rename = "Bundler version")]
     pub(crate) version: ResolvedBundlerVersion,
diff --git a/buildpacks/ruby/src/layers/bundle_install_layer.rs b/buildpacks/ruby/src/layers/bundle_install_layer.rs
index 6344f3c3..7dca1f19 100644
--- a/buildpacks/ruby/src/layers/bundle_install_layer.rs
+++ b/buildpacks/ruby/src/layers/bundle_install_layer.rs
@@ -125,6 +125,7 @@ try_migrate_deserializer_chain!(
 );
 
 #[derive(Deserialize, Serialize, Debug, Clone, Eq, PartialEq)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct MetadataV1 {
     pub(crate) stack: String,
     pub(crate) ruby_version: ResolvedRubyVersion,
@@ -133,6 +134,7 @@ pub(crate) struct MetadataV1 {
 }
 
 #[derive(Deserialize, Serialize, Debug, Clone, Eq, PartialEq)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct MetadataV2 {
     pub(crate) distro_name: String,
     pub(crate) distro_version: String,
@@ -315,6 +317,7 @@ fn display_name(cmd: &mut Command, env: &Env) -> String {
 }
 
 #[derive(Deserialize, Serialize, Debug, Clone, Eq, PartialEq, Default)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct BundleDigest {
     env: String,
     gemfile: String,
diff --git a/buildpacks/ruby/src/layers/metrics_agent_install.rs b/buildpacks/ruby/src/layers/metrics_agent_install.rs
index 2543f843..2c289194 100644
--- a/buildpacks/ruby/src/layers/metrics_agent_install.rs
+++ b/buildpacks/ruby/src/layers/metrics_agent_install.rs
@@ -30,6 +30,7 @@ const DOWNLOAD_URL: &str =
 const DOWNLOAD_SHA: &str = "f9bf9f33c949e15ffed77046ca38f8dae9307b6a0181c6af29a25dec46eb2dac";
 
 #[derive(Deserialize, Serialize, Debug, Clone, PartialEq, Eq)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct Metadata {
     download_url: String,
 }
diff --git a/buildpacks/ruby/src/layers/ruby_install_layer.rs b/buildpacks/ruby/src/layers/ruby_install_layer.rs
index 8d72b6d0..229512ee 100644
--- a/buildpacks/ruby/src/layers/ruby_install_layer.rs
+++ b/buildpacks/ruby/src/layers/ruby_install_layer.rs
@@ -76,12 +76,14 @@ fn install_ruby(metadata: &Metadata, layer_path: &Path) -> Result<(), RubyBuildp
 }
 
 #[derive(Deserialize, Serialize, Debug, Clone)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct MetadataV1 {
     pub(crate) stack: String,
     pub(crate) version: ResolvedRubyVersion,
 }
 
 #[derive(Deserialize, Serialize, Debug, Clone, Eq, PartialEq)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct MetadataV2 {
     pub(crate) distro_name: String,
     pub(crate) distro_version: String,
diff --git a/commons/src/cache/app_cache.rs b/commons/src/cache/app_cache.rs
index 773cb9c9..395aa138 100644
--- a/commons/src/cache/app_cache.rs
+++ b/commons/src/cache/app_cache.rs
@@ -251,6 +251,7 @@ pub enum PathState {
 ///  allows for emails, that might live a long time, to reference a specific SHA of an
 ///  asset.
 #[derive(Deserialize, Serialize, Debug, Clone, PartialEq, Eq)]
+#[serde(deny_unknown_fields)]
 pub(crate) struct Metadata {
     pub(crate) app_dir_path: PathBuf,
 }
diff --git a/commons/src/metadata_digest.rs b/commons/src/metadata_digest.rs
index 2f9ce418..04f1e016 100644
--- a/commons/src/metadata_digest.rs
+++ b/commons/src/metadata_digest.rs
@@ -20,6 +20,7 @@ const PLATFORM_ENV_VAR: &str = "user configured environment variables";
 /// use commons::metadata_digest::MetadataDigest;
 ///
 /// #[derive(Deserialize, Serialize, Debug, Clone, Eq, PartialEq)]
+/// #[serde(deny_unknown_fields)]
 /// pub(crate) struct BundleInstallLayerMetadata {
 ///     ruby_version: String,
 ///     force_bundle_install_key: String,
@@ -82,6 +83,7 @@ const PLATFORM_ENV_VAR: &str = "user configured environment variables";
 /// # }
 /// #
 /// # #[derive(Deserialize, Serialize, Debug, Clone, Eq, PartialEq)]
+/// # #[serde(deny_unknown_fields)]
 /// # struct FakeLayerMetadata {
 /// #     digest: MetadataDigest,
 /// # }