diff --git a/Lib/test/test_capi/test_opt.py b/Lib/test/test_capi/test_opt.py
index 36efab518781410..6721439a2fb2f45 100644
--- a/Lib/test/test_capi/test_opt.py
+++ b/Lib/test/test_capi/test_opt.py
@@ -12,7 +12,8 @@
 
 from test.support import (script_helper, requires_specialization,
                           import_helper, Py_GIL_DISABLED, requires_jit_enabled,
-                          reset_code, SHORT_TIMEOUT, isolation)
+                          reset_code, SHORT_TIMEOUT, isolation,
+                          threading_helper)
 
 _testinternalcapi = import_helper.import_module("_testinternalcapi")
 
@@ -6268,6 +6269,34 @@ def exhaust(iterator):
         # A different iterator type must not link that executor to itself.
         exhaust(map(bool, values))
 
+    @isolation.runInSubprocess(
+            env={'PYTHON_JIT': '1', 'PYTHON_JIT_STRESS': '1'},
+            timeout=SHORT_TIMEOUT)
+    def test_157740_stale_oparg_executor_race(self):
+        import json
+        import threading
+
+        sys.setswitchinterval(1e-6)
+
+        def worker(data, index):
+            while data:
+                for d in list(data):
+                    d[index] = index
+
+        for _ in range(25):
+            # Race executor installation against tracing the same code.
+            worker.__code__ = worker.__code__.replace()
+            data = [{}, {}]
+            threads = [threading.Thread(target=worker, args=(data, i),
+                                        daemon=True)
+                       for i in range(4)]
+            with threading_helper.start_threads(threads, unlock=data.clear):
+                for _ in range(200):
+                    try:
+                        json.dumps(data)
+                    except Exception:
+                        pass
+
 def global_identity(x):
     return x
 
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-09-20-11-58-15.gh-issue-157740.S3wLtW.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-09-20-11-58-15.gh-issue-157740.S3wLtW.rst
new file mode 100644
index 000000000000000..00b2afbb9e34c4e
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-09-20-11-58-15.gh-issue-157740.S3wLtW.rst
@@ -0,0 +1 @@
+Fix a crash when multiple threads execute the same code with the JIT enabled. A stale ``oparg`` value could be used as an executor index, causing an out-of-bounds read.
diff --git a/Python/optimizer.c b/Python/optimizer.c
index e05adb344c8d06d..48b2b570f2588b6 100644
--- a/Python/optimizer.c
+++ b/Python/optimizer.c
@@ -706,7 +706,7 @@ _PyJit_translate_single_bytecode_to_trace(
     }
 
     if (opcode == ENTER_EXECUTOR) {
-        _PyExecutorObject *executor = old_code->co_executors->executors[oparg & 255];
+        _PyExecutorObject *executor = old_code->co_executors->executors[this_instr->op.arg];
         opcode = executor->vm_data.opcode;
         oparg = (oparg & ~255) | executor->vm_data.oparg;
     }