diff --git a/codex-rs/core/src/hook_runtime.rs b/codex-rs/core/src/hook_runtime.rs
index d9064756e8..8acaee6a52 100644
--- a/codex-rs/core/src/hook_runtime.rs
+++ b/codex-rs/core/src/hook_runtime.rs
@@ -128,9 +128,7 @@ pub(crate) async fn run_pending_session_start_hooks(
             .run_session_start(request, Some(turn_context.sub_id.clone()))
             .await;
         emit_hook_completed_events(sess, turn_context, hook_events).await;
-        if let Some(env) = session_start_env {
-            sess.merge_session_start_env(env);
-        }
+        sess.merge_session_start_env(session_start_env);
         record_additional_contexts(sess, turn_context, additional_contexts).await;
         if should_stop {
             return true;
diff --git a/codex-rs/hooks/src/events/session_start.rs b/codex-rs/hooks/src/events/session_start.rs
index c51028bb3b..22479b05a8 100644
--- a/codex-rs/hooks/src/events/session_start.rs
+++ b/codex-rs/hooks/src/events/session_start.rs
@@ -83,7 +83,7 @@ pub struct SessionStartOutcome {
     pub should_stop: bool,
     pub stop_reason: Option<String>,
     pub additional_contexts: Vec<String>,
-    pub session_start_env: Option<HashMap<String, String>>,
+    pub session_start_env: HashMap<String, String>,
 }
 
 #[derive(Debug, PartialEq, Eq)]
@@ -123,7 +123,7 @@ pub(crate) async fn run(
             should_stop: false,
             stop_reason: None,
             additional_contexts: Vec::new(),
-            session_start_env: session_start_env_for_event(event_name),
+            session_start_env: HashMap::new(),
         };
     }
 
@@ -145,7 +145,6 @@ pub(crate) async fn run(
                             turn_id,
                             format!("failed to serialize session start hook input: {error}"),
                         ),
-                        event_name,
                     );
                 }
             };
@@ -176,7 +175,6 @@ pub(crate) async fn run(
                             Some(subagent_turn_id),
                             format!("failed to serialize subagent start hook input: {error}"),
                         ),
-                        event_name,
                     );
                 }
             };
@@ -203,9 +201,8 @@ pub(crate) async fn run(
             .iter()
             .map(|result| result.data.additional_contexts_for_model.as_slice()),
     );
-    let session_start_env = (event_name == HookEventName::SessionStart).then(|| {
-        merge_session_start_env(results.iter().map(|result| &result.data.session_start_env))
-    });
+    let session_start_env =
+        merge_session_start_env(results.iter().map(|result| &result.data.session_start_env));
 
     SessionStartOutcome {
         hook_events: results.into_iter().map(|result| result.completed).collect(),
@@ -353,23 +350,16 @@ fn parse_completed(
     }
 }
 
-fn serialization_failure_outcome(
-    hook_events: Vec<HookCompletedEvent>,
-    event_name: HookEventName,
-) -> SessionStartOutcome {
+fn serialization_failure_outcome(hook_events: Vec<HookCompletedEvent>) -> SessionStartOutcome {
     SessionStartOutcome {
         hook_events,
         should_stop: false,
         stop_reason: None,
         additional_contexts: Vec::new(),
-        session_start_env: session_start_env_for_event(event_name),
+        session_start_env: HashMap::new(),
     }
 }
 
-fn session_start_env_for_event(event_name: HookEventName) -> Option<HashMap<String, String>> {
-    (event_name == HookEventName::SessionStart).then(HashMap::new)
-}
-
 fn merge_session_start_env<'a>(
     envs: impl IntoIterator<Item = &'a HashMap<String, String>>,
 ) -> HashMap<String, String> {