diff --git a/Python/instrumentation.c b/Python/instrumentation.c
index a7a5b4a5dc5..f77c2e696f4 100644
--- a/Python/instrumentation.c
+++ b/Python/instrumentation.c
@@ -564,6 +564,7 @@ de_instrument(PyCodeObject *code, int i, int event)
     _Py_CODEUNIT *instr = &_PyCode_CODE(code)[i];
     uint8_t *opcode_ptr = &instr->op.code;
     int opcode = *opcode_ptr;
+    assert(opcode != ENTER_EXECUTOR);
     if (opcode == INSTRUMENTED_LINE) {
         opcode_ptr = &code->_co_monitoring->lines[i].original_opcode;
         opcode = *opcode_ptr;