diff --git a/Python/specialize.c b/Python/specialize.c
index a467f163f2ca9d..fac3c3ea57d004 100644
--- a/Python/specialize.c
+++ b/Python/specialize.c
@@ -300,6 +300,8 @@ _PyCode_Quicken(PyCodeObject *code)
     for (int i = 0; i < Py_SIZE(code); i++) {
         opcode = _Py_GetBaseOpcode(code, i);
         assert(opcode < MIN_INSTRUMENTED_OPCODE);
+        // _PyCode_Quicken is only called when initializing a fresh code object.
+        assert(opcode != ENTER_EXECUTOR);
         int caches = _PyOpcode_Caches[opcode];
         if (caches) {
             instructions[i + 1].cache = adaptive_counter_warmup();