diff --git a/include/pocketpy/objects/base.h b/include/pocketpy/objects/base.h
index d8e74276..d1ac55b5 100644
--- a/include/pocketpy/objects/base.h
+++ b/include/pocketpy/objects/base.h
@@ -31,3 +31,4 @@ typedef struct py_TValue {
 // 16 bytes to make py_arg() macro work
 static_assert(sizeof(py_CFunction) <= 8, "sizeof(py_CFunction) > 8");
 static_assert(sizeof(py_TValue) == 16, "sizeof(py_TValue) != 16");
+static_assert(offsetof(py_TValue, extra) == 4, "offsetof(py_TValue, extra) != 4");
\ No newline at end of file