diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index cbb1b92..9cd3ad8 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -213,6 +213,11 @@
                 self.assertEqual(result, list(cwr1(values, r)))         # matches first pure python version
                 self.assertEqual(result, list(cwr2(values, r)))         # matches second pure python version
 
+    @test_support.bigaddrspacetest
+    def test_combinations_with_replacement_overflow(self):
+        with self.assertRaises(OverflowError):
+            combinations_with_replacement("AA", 2**30)
+
     @test_support.impl_detail("tuple reuse is specific to CPython")
     def test_combinations_with_replacement_tuple_reuse(self):
         cwr = combinations_with_replacement
diff --git a/Misc/NEWS b/Misc/NEWS
index 87a1d9f..b213a29 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -18,6 +18,9 @@
 Library
 -------
 
+- Issue #23365: Fixed possible integer overflow in
+  itertools.combinations_with_replacement.
+
 - Issue #23366: Fixed possible integer overflow in itertools.combinations.
 
 - Issue #23191: fnmatch functions that use caching are now threadsafe.
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 4eab79c..47a5e8b 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -2346,6 +2346,10 @@
         goto error;
     }
 
+    if (r > PY_SSIZE_T_MAX/sizeof(Py_ssize_t)) {
+        PyErr_SetString(PyExc_OverflowError, "r is too big");
+        goto error;
+    }
     indices = PyMem_Malloc(r * sizeof(Py_ssize_t));
     if (indices == NULL) {
         PyErr_NoMemory();