diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index d5129bf6a5a6bc..fbdd637a3fcb78 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -3046,7 +3046,7 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
                     return NULL;
                 }
             }
-            if (PyFloat_Check(item)) {
+            if (PyFloat_CheckExact(item)) {
                 double value = PyFloat_AS_DOUBLE(item);
                 re_sum = cs_add(re_sum, value);
                 _Py_DECREF_SPECIALIZED(item, _PyFloat_ExactDealloc);