diff --git a/codex-rs/core/src/seatbelt_base_policy.sbpl b/codex-rs/core/src/seatbelt_base_policy.sbpl
index 824e02803..8ccfa6e82 100644
--- a/codex-rs/core/src/seatbelt_base_policy.sbpl
+++ b/codex-rs/core/src/seatbelt_base_policy.sbpl
@@ -53,6 +53,7 @@
   (sysctl-name "hw.physicalcpu_max")
   (sysctl-name "hw.tbfrequency_compat")
   (sysctl-name "hw.vectorunit")
+  (sysctl-name "kern.argmax")
   (sysctl-name "kern.hostname")
   (sysctl-name "kern.maxfilesperproc")
   (sysctl-name "kern.maxproc")
@@ -72,7 +73,8 @@
   (sysctl-name-prefix "net.routetable.")
 )
 
-; Allow Java to set CPU type grade when required
+; Allow Java to read some CPU info. This is misclassified as a "write" because
+; userspace passes a memory buffer to the sysctl, but conceptually it is a read.
 (allow sysctl-write
   (sysctl-name "kern.grade_cputype"))
 
@@ -86,10 +88,17 @@
   (global-name "com.apple.system.opendirectoryd.libinfo")
 )
 
-; Added on top of Chrome profile
 ; Needed for python multiprocessing on MacOS for the SemLock
 (allow ipc-posix-sem)
 
 (allow mach-lookup
   (global-name "com.apple.PowerManagement.control")
 )
+
+; allow openpty()
+(allow pseudo-tty)
+(allow file-read* file-write* file-ioctl (literal "/dev/ptmx"))
+(allow file-read* file-write*
+  (require-all
+    (regex #"^/dev/ttys[0-9]+")
+    (extension "com.apple.sandbox.pty")))
diff --git a/codex-rs/core/tests/suite/seatbelt.rs b/codex-rs/core/tests/suite/seatbelt.rs
index 53175fca1..52150b051 100644
--- a/codex-rs/core/tests/suite/seatbelt.rs
+++ b/codex-rs/core/tests/suite/seatbelt.rs
@@ -159,23 +159,18 @@ async fn read_only_forbids_all_writes() {
         .await;
 }
 
-/// Verify that user lookups via `pwd.getpwuid(os.getuid())` work under the
-/// seatbelt sandbox. Prior to allowing the necessary mach‑lookup for
-/// OpenDirectory libinfo, this would fail with `KeyError: getpwuid(): uid not found`.
 #[tokio::test]
-async fn python_getpwuid_works_under_seatbelt() {
+async fn openpty_works_under_seatbelt() {
     if std::env::var(CODEX_SANDBOX_ENV_VAR) == Ok("seatbelt".to_string()) {
         eprintln!("{CODEX_SANDBOX_ENV_VAR} is set to 'seatbelt', skipping test.");
         return;
     }
 
-    // For local dev.
     if which::which("python3").is_err() {
         eprintln!("python3 not found in PATH, skipping test.");
         return;
     }
 
-    // ReadOnly is sufficient here since we are only exercising user lookup.
     let policy = SandboxPolicy::ReadOnly;
     let command_cwd = std::env::current_dir().expect("getcwd");
     let sandbox_cwd = command_cwd.clone();
@@ -184,8 +179,12 @@ async fn python_getpwuid_works_under_seatbelt() {
         vec![
             "python3".to_string(),
             "-c".to_string(),
-            // Print the passwd struct; success implies lookup worked.
-            "import pwd, os; print(pwd.getpwuid(os.getuid()))".to_string(),
+            r#"import os
+
+master, slave = os.openpty()
+os.write(slave, b"ping")
+assert os.read(master, 4) == b"ping""#
+                .to_string(),
         ],
         command_cwd,
         &policy,
diff --git a/codex-rs/exec/tests/suite/sandbox.rs b/codex-rs/exec/tests/suite/sandbox.rs
index 73a7f0d5b..f0faa8b43 100644
--- a/codex-rs/exec/tests/suite/sandbox.rs
+++ b/codex-rs/exec/tests/suite/sandbox.rs
@@ -109,6 +109,45 @@ if __name__ == '__main__':
     assert!(status.success(), "python exited with {status:?}");
 }
 
+#[tokio::test]
+async fn python_getpwuid_works_under_sandbox() {
+    core_test_support::skip_if_sandbox!();
+
+    if std::process::Command::new("python3")
+        .arg("--version")
+        .status()
+        .is_err()
+    {
+        eprintln!("python3 not found in PATH, skipping test.");
+        return;
+    }
+
+    let policy = SandboxPolicy::ReadOnly;
+    let command_cwd = std::env::current_dir().expect("should be able to get current dir");
+    let sandbox_cwd = command_cwd.clone();
+
+    let mut child = spawn_command_under_sandbox(
+        vec![
+            "python3".to_string(),
+            "-c".to_string(),
+            "import pwd, os; print(pwd.getpwuid(os.getuid()))".to_string(),
+        ],
+        command_cwd,
+        &policy,
+        sandbox_cwd.as_path(),
+        StdioPolicy::RedirectForShellTool,
+        HashMap::new(),
+    )
+    .await
+    .expect("should be able to spawn python under sandbox");
+
+    let status = child
+        .wait()
+        .await
+        .expect("should be able to wait for child process");
+    assert!(status.success(), "python exited with {status:?}");
+}
+
 #[tokio::test]
 async fn sandbox_distinguishes_command_and_policy_cwds() {
     core_test_support::skip_if_sandbox!();