https://github.com/python/cpython/issues/127344

--- Python-3.14.0/Modules/socketmodule.c.orig
+++ Python-3.14.0/Modules/socketmodule.c
@@ -3342,6 +3342,7 @@
     int optname;
     int res;
     Py_buffer optval;
+    int buflen;
     int flag;
     unsigned int optlen;
     PyObject *none;
@@ -3375,8 +3376,15 @@
             goto done;
         }
 #endif
+
+        buflen = sizeof flag;
+        /* Multi cast options take shorter arguments */
+        if (optname == IP_MULTICAST_TTL
+            || optname == IP_MULTICAST_LOOP)
+                buflen = sizeof(u_char);
+
         res = setsockopt(get_sock_fd(s), level, optname,
-                         (char*)&flag, sizeof flag);
+                         (char*)&flag, buflen);
         goto done;
     }