diff --git a/test/libc/sock/multicast_test.c b/test/libc/sock/multicast_test.c
new file mode 100644
index 000000000..bce61d4eb
--- /dev/null
+++ b/test/libc/sock/multicast_test.c
@@ -0,0 +1,106 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/atomic.h"
+#include "libc/calls/calls.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sock/sock.h"
+#include "libc/sock/struct/ip_mreq.h"
+#include "libc/sock/struct/sockaddr.h"
+#include "libc/sysv/consts/af.h"
+#include "libc/sysv/consts/inaddr.h"
+#include "libc/sysv/consts/ip.h"
+#include "libc/sysv/consts/ipproto.h"
+#include "libc/sysv/consts/so.h"
+#include "libc/sysv/consts/sock.h"
+#include "libc/sysv/consts/sol.h"
+#include "libc/testlib/subprocess.h"
+#include "libc/testlib/testlib.h"
+
+struct Shared {
+  atomic_int ready;
+  atomic_int isworking;
+} * g_shared;
+
+void Receiver(void) {
+  int y = 1;
+  char buf[8];
+  struct sockaddr_in addr = {
+      .sin_family = AF_INET,
+      .sin_port = htons(31337),
+      .sin_addr.s_addr = INADDR_ANY,
+  };
+  struct ip_mreq group = {
+      .imr_multiaddr.s_addr = inet_addr("224.0.0.251"),
+      .imr_interface.s_addr = INADDR_ANY,
+  };
+  EXPECT_SYS(0, 3, socket(AF_INET, SOCK_DGRAM, 0));
+  EXPECT_SYS(0, 0, setsockopt(3, SOL_SOCKET, SO_REUSEADDR, &y, sizeof(y)));
+  EXPECT_SYS(0, 0, bind(3, (struct sockaddr *)&addr, sizeof(addr)));
+  EXPECT_SYS(0, 0,
+             setsockopt(3, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group,
+                        sizeof(group)));
+  g_shared->isworking = !g_testlib_failed;
+  g_shared->ready = 1;
+  if (g_shared->isworking) {
+    ASSERT_SYS(0, 8, read(3, buf, 8));
+  }
+  ASSERT_SYS(0, 0, close(3));
+}
+
+void Sender(void) {
+  int y = 1;
+  char buf[8];
+  struct sockaddr_in addr = {
+      .sin_family = AF_INET,
+      .sin_port = htons(31337),
+      .sin_addr.s_addr = INADDR_ANY,
+  };
+  struct sockaddr_in dest = {
+      .sin_family = AF_INET,
+      .sin_port = htons(31337),
+      .sin_addr.s_addr = inet_addr("224.0.0.251"),
+  };
+  struct ip_mreq group = {
+      .imr_multiaddr.s_addr = inet_addr("224.0.0.251"),
+      .imr_interface.s_addr = INADDR_ANY,
+  };
+  ASSERT_SYS(0, 3, socket(AF_INET, SOCK_DGRAM, 0));
+  ASSERT_SYS(0, 0, setsockopt(3, SOL_SOCKET, SO_REUSEADDR, &y, sizeof(y)));
+  ASSERT_SYS(0, 0, bind(3, (struct sockaddr *)&addr, sizeof(addr)));
+  ASSERT_SYS(0, 0,
+             setsockopt(3, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group,
+                        sizeof(group)));
+  ASSERT_SYS(0, 8,
+             sendto(3, buf, 8, 0, (struct sockaddr *)&dest, sizeof(dest)));
+  ASSERT_SYS(0, 0, close(3));
+}
+
+TEST(multicast, test) {
+  ASSERT_NE(NULL, (g_shared = _mapshared(FRAMESIZE)));
+  SPAWN(fork);
+  Receiver();
+  PARENT();
+  while (!g_shared->ready) {
+  }
+  if (g_shared->isworking) {
+    Sender();
+  }
+  WAIT(exit, 0);
+  munmap(g_shared, FRAMESIZE);
+}
diff --git a/test/libc/sock/test.mk b/test/libc/sock/test.mk
index 1cdc64d55..843f56d51 100644
--- a/test/libc/sock/test.mk
+++ b/test/libc/sock/test.mk
@@ -82,6 +82,11 @@ o/$(MODE)/test/libc/sock/recvmsg_test.com.runs:			\
 o/$(MODE)/test/libc/sock/shutdown_test.com.runs:		\
 		private .PLEDGE = stdio rpath wpath cpath fattr proc inet
 
+o/$(MODE)/test/libc/sock/multicast_test.com.runs:		\
+		private .UNSANDBOXED = 1
+o/$(MODE)/test/libc/sock/multicast_test.com.runs:		\
+		private .INTERNET = 1
+
 $(TEST_LIBC_SOCK_OBJS): test/libc/sock/test.mk
 
 .PHONY: o/$(MODE)/test/libc/sock