diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index f99ebf0dde..24044c5113 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -3312,6 +3312,109 @@ function_set_warning(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     Py_RETURN_NONE;
 }
 
+static PyObject *
+bench_concat(PyObject *Py_UNUSED(module), PyObject *args)
+{
+    Py_ssize_t loops;
+    if (!PyArg_ParseTuple(args, "n", &loops)) {
+        return NULL;
+    }
+
+    PyObject *a = PyUnicode_FromString("x");
+    PyObject *b = PyUnicode_FromString("=");
+    PyObject *ch = PyUnicode_FromString("\"");
+    PyObject *c = PyUnicode_FromString("string value");
+    PyObject *sep = PyUnicode_FromString(", ");
+    assert(a != NULL && b != NULL && ch != NULL && c != NULL && sep != NULL);
+
+    PyTime_t t1;
+    (void)PyTime_PerfCounterRaw(&t1);
+
+    for (Py_ssize_t i=0; i < loops; i++) {
+        PyObject *str = PyUnicode_Concat(a, b);
+        assert(str != NULL);
+
+        for (int j=0; j<10; j++) {
+            if (j != 0) {
+                PyUnicode_Append(&str, sep);
+                assert(str != NULL);
+            }
+            PyUnicode_Append(&str, ch);
+            assert(str != NULL);
+            PyUnicode_Append(&str, c);
+            assert(str != NULL);
+            PyUnicode_Append(&str, ch);
+            assert(str != NULL);
+        }
+
+        Py_DECREF(str);
+    }
+
+    PyTime_t t2;
+    (void)PyTime_PerfCounterRaw(&t2);
+
+    Py_DECREF(a);
+    Py_DECREF(b);
+    Py_DECREF(ch);
+    Py_DECREF(c);
+    Py_DECREF(sep);
+
+    return PyFloat_FromDouble(PyTime_AsSecondsDouble(t2 - t1));
+}
+
+static PyObject *
+bench_writer(PyObject *Py_UNUSED(module), PyObject *args)
+{
+    Py_ssize_t loops;
+    if (!PyArg_ParseTuple(args, "n", &loops)) {
+        return NULL;
+    }
+
+    PyObject *a = PyUnicode_FromString("x");
+    PyObject *b = PyUnicode_FromString("=");
+    PyObject *sep = PyUnicode_FromString(", ");
+    PyObject *c = PyUnicode_FromString("string value");
+    assert(a != NULL && b != NULL && sep != NULL && c != NULL);
+
+    PyTime_t t1;
+    (void)PyTime_PerfCounterRaw(&t1);
+
+    for (Py_ssize_t i=0; i < loops; i++) {
+        PyUnicodeWriter *writer = PyUnicodeWriter_Create();
+        // Overallocation is enabled by default
+
+        assert(PyUnicodeWriter_WriteStr(writer, a) == 0);
+        assert(PyUnicodeWriter_WriteChar(writer, '=') == 0);
+
+        for (int j=0; j<10; j++) {
+            if (j != 0) {
+                assert(PyUnicodeWriter_WriteStr(writer, sep) == 0);
+            }
+            assert(PyUnicodeWriter_WriteChar(writer, '"') == 0);
+            assert(PyUnicodeWriter_WriteStr(writer, c) == 0);
+            if (j == 9) {
+                // Disable overallocation before the last write
+                PyUnicodeWriter_SetOverallocate(writer, 0);
+            }
+            assert(PyUnicodeWriter_WriteChar(writer, '"') == 0);
+        }
+
+        PyObject *str = PyUnicodeWriter_Finish(writer);
+        assert(str != NULL);
+        Py_DECREF(str);
+    }
+
+    PyTime_t t2;
+    (void)PyTime_PerfCounterRaw(&t2);
+
+    Py_DECREF(a);
+    Py_DECREF(b);
+    Py_DECREF(sep);
+    Py_DECREF(c);
+
+    return PyFloat_FromDouble(PyTime_AsSecondsDouble(t2 - t1));
+}
+
 static PyMethodDef TestMethods[] = {
     {"set_errno",               set_errno,                       METH_VARARGS},
     {"test_config",             test_config,                     METH_NOARGS},
@@ -3454,6 +3557,8 @@ static PyMethodDef TestMethods[] = {
     {"check_pyimport_addmodule", check_pyimport_addmodule, METH_VARARGS},
     {"test_weakref_capi", test_weakref_capi, METH_NOARGS},
     {"function_set_warning", function_set_warning, METH_NOARGS},
+    {"bench_concat", bench_concat, METH_VARARGS},
+    {"bench_writer", bench_writer, METH_VARARGS},
     {NULL, NULL} /* sentinel */
 };
 
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 8646664532..6a590aa734 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -13115,6 +13115,7 @@ PyUnicodeWriter_Create(void)
         return NULL;
     }
     _PyUnicodeWriter_Init((_PyUnicodeWriter*)writer);
+    PyUnicodeWriter_SetOverallocate(writer, 1);
     return writer;
 }