diff --git a/codex-rs/cli/src/main.rs b/codex-rs/cli/src/main.rs
index 940e1e536d..90d6440cf4 100644
--- a/codex-rs/cli/src/main.rs
+++ b/codex-rs/cli/src/main.rs
@@ -29,6 +29,7 @@ mod mcp_cmd;
 use crate::mcp_cmd::McpCli;
 use codex_core::config::Config;
 use codex_core::config::ConfigOverrides;
+use codex_core::features::is_known_feature_key;
 
 /// Codex CLI
 ///
@@ -286,15 +287,25 @@ struct FeatureToggles {
 }
 
 impl FeatureToggles {
-    fn to_overrides(&self) -> Vec<String> {
+    fn to_overrides(&self) -> anyhow::Result<Vec<String>> {
         let mut v = Vec::new();
-        for k in &self.enable {
-            v.push(format!("features.{k}=true"));
+        for feature in &self.enable {
+            Self::validate_feature(feature)?;
+            v.push(format!("features.{feature}=true"));
         }
-        for k in &self.disable {
-            v.push(format!("features.{k}=false"));
+        for feature in &self.disable {
+            Self::validate_feature(feature)?;
+            v.push(format!("features.{feature}=false"));
+        }
+        Ok(v)
+    }
+
+    fn validate_feature(feature: &str) -> anyhow::Result<()> {
+        if is_known_feature_key(feature) {
+            Ok(())
+        } else {
+            anyhow::bail!("Unknown feature flag: {feature}")
         }
-        v
     }
 }
 
@@ -345,9 +356,8 @@ async fn cli_main(codex_linux_sandbox_exe: Option<PathBuf>) -> anyhow::Result<()
     } = MultitoolCli::parse();
 
     // Fold --enable/--disable into config overrides so they flow to all subcommands.
-    root_config_overrides
-        .raw_overrides
-        .extend(feature_toggles.to_overrides());
+    let toggle_overrides = feature_toggles.to_overrides()?;
+    root_config_overrides.raw_overrides.extend(toggle_overrides);
 
     match subcommand {
         None => {
@@ -605,6 +615,7 @@ mod tests {
     use assert_matches::assert_matches;
     use codex_core::protocol::TokenUsage;
     use codex_protocol::ConversationId;
+    use pretty_assertions::assert_eq;
 
     fn finalize_from_args(args: &[&str]) -> TuiCli {
         let cli = MultitoolCli::try_parse_from(args).expect("parse");
@@ -781,4 +792,32 @@ mod tests {
         assert!(!interactive.resume_last);
         assert_eq!(interactive.resume_session_id, None);
     }
+
+    #[test]
+    fn feature_toggles_known_features_generate_overrides() {
+        let toggles = FeatureToggles {
+            enable: vec!["web_search_request".to_string()],
+            disable: vec!["unified_exec".to_string()],
+        };
+        let overrides = toggles.to_overrides().expect("valid features");
+        assert_eq!(
+            overrides,
+            vec![
+                "features.web_search_request=true".to_string(),
+                "features.unified_exec=false".to_string(),
+            ]
+        );
+    }
+
+    #[test]
+    fn feature_toggles_unknown_feature_errors() {
+        let toggles = FeatureToggles {
+            enable: vec!["does_not_exist".to_string()],
+            disable: Vec::new(),
+        };
+        let err = toggles
+            .to_overrides()
+            .expect_err("feature should be rejected");
+        assert_eq!(err.to_string(), "Unknown feature flag: does_not_exist");
+    }
 }
diff --git a/codex-rs/core/src/features.rs b/codex-rs/core/src/features.rs
index c10305b800..269a445203 100644
--- a/codex-rs/core/src/features.rs
+++ b/codex-rs/core/src/features.rs
@@ -191,6 +191,11 @@ fn feature_for_key(key: &str) -> Option<Feature> {
     legacy::feature_for_key(key)
 }
 
+/// Returns `true` if the provided string matches a known feature toggle key.
+pub fn is_known_feature_key(key: &str) -> bool {
+    feature_for_key(key).is_some()
+}
+
 /// Deserializable features table for TOML.
 #[derive(Deserialize, Debug, Clone, Default, PartialEq)]
 pub struct FeaturesToml {