diff --git a/src/backend/kqueue.zig b/src/backend/kqueue.zig
index a78249dd..7b7f717d 100644
--- a/src/backend/kqueue.zig
+++ b/src/backend/kqueue.zig
@@ -1247,8 +1247,8 @@ pub const Completion = struct {
                         const ev = ev_ orelse
                             break :res .{ .read = error.MissingKevent };
                         break :empty @intCast(ev.data);
-                    } else xev_posix.recvfrom(op.fd, v, 0, &op.addr, &op.addr_size) catch |err| mapReadError(err),
-                    .array => |*v| xev_posix.recvfrom(op.fd, v, 0, &op.addr, &op.addr_size) catch |err| mapReadError(err),
+                    } else xev_posix.recvfrom(op.fd, v, 0, @ptrCast(&op.addr), &op.addr_size) catch |err| mapReadError(err),
+                    .array => |*v| xev_posix.recvfrom(op.fd, v, 0, @ptrCast(&op.addr), &op.addr_size) catch |err| mapReadError(err),
                 };
 
                 break :res .{
@@ -1652,8 +1652,11 @@ pub const Operation = union(OperationType) {
     recvfrom: struct {
         fd: posix.fd_t,
         buffer: ReadBuffer,
-        addr: posix.sockaddr = undefined,
-        addr_size: posix.socklen_t = @sizeOf(posix.sockaddr),
+        /// Room for an IPv4 or IPv6 source. A posix.sockaddr is too small
+        /// for a sockaddr_in6; a sockaddr_storage would push Completion
+        /// past its size limit.
+        addr: posix.sockaddr.in6 = undefined,
+        addr_size: posix.socklen_t = @sizeOf(posix.sockaddr.in6),
     },
 
     close: struct {
diff --git a/src/watcher/udp.zig b/src/watcher/udp.zig
index a480e9ed..301fe4a5 100644
--- a/src/watcher/udp.zig
+++ b/src/watcher/udp.zig
@@ -134,7 +134,7 @@ fn UDPSendto(comptime xev: type) type {
                                     l_inner,
                                     c_inner,
                                     s_inner,
-                                    net.Address.initPosix(@alignCast(&c_inner.op.recvfrom.addr)).toIpAddress(),
+                                    net.Address.initPosix(@ptrCast(&c_inner.op.recvfrom.addr)).toIpAddress(),
                                     initFd(c_inner.op.recvfrom.fd),
                                     c_inner.op.recvfrom.buffer,
                                     r.recvfrom,
@@ -924,6 +924,80 @@ fn UDPTests(comptime xev: type, comptime Impl: type) type {
             }
         }
 
+        test "UDP: read reports the source address of an IPv6 sender" {
+            if (builtin.os.tag == .freebsd) return error.SkipZigTest;
+            // The IOCP backend's recvfrom has not been checked for this.
+            if (builtin.os.tag == .windows) return error.SkipZigTest;
+            const testing = std.testing;
+
+            var tpool = ThreadPool.init(.{});
+            defer tpool.deinit();
+            defer tpool.shutdown();
+            var loop = try xev.Loop.init(.{ .thread_pool = &tpool });
+            defer loop.deinit();
+
+            const address = try std.Io.net.IpAddress.parse("::1", 3133);
+            const server = Impl.init(address) catch return error.SkipZigTest;
+            server.bind(address) catch return error.SkipZigTest; // no IPv6 loopback
+            const client = try Impl.init(address);
+
+            const Received = struct { len: usize = 0, from: ?std.Io.net.IpAddress = null };
+            var received: Received = .{};
+            var c_read: xev.Completion = undefined;
+            var s_read: Impl.State = undefined;
+            var recv_buf: [128]u8 = undefined;
+            server.read(&loop, &c_read, &s_read, .{ .slice = &recv_buf }, Received, &received, (struct {
+                fn callback(
+                    ud: ?*Received,
+                    _: *xev.Loop,
+                    _: *xev.Completion,
+                    _: *Impl.State,
+                    addr: std.Io.net.IpAddress,
+                    _: Impl,
+                    _: xev.ReadBuffer,
+                    r: xev.ReadError!usize,
+                ) xev.CallbackAction {
+                    ud.?.len = r catch unreachable;
+                    ud.?.from = addr;
+                    return .disarm;
+                }
+            }).callback);
+
+            var send_buf = [_]u8{ 1, 2, 3 };
+            var c_write: xev.Completion = undefined;
+            var s_write: Impl.State = undefined;
+            client.write(&loop, &c_write, &s_write, address, .{ .slice = &send_buf }, void, null, (struct {
+                fn callback(
+                    _: ?*void,
+                    _: *xev.Loop,
+                    _: *xev.Completion,
+                    _: *Impl.State,
+                    _: Impl,
+                    _: xev.WriteBuffer,
+                    r: xev.WriteError!usize,
+                ) xev.CallbackAction {
+                    _ = r catch unreachable;
+                    return .disarm;
+                }
+            }).callback);
+
+            try loop.run(.until_done);
+            try testing.expectEqual(@as(usize, 3), received.len);
+            const loopback: [16]u8 = .{0} ** 15 ++ .{1};
+            try testing.expectEqualSlices(u8, &loopback, &received.from.?.ip6.bytes);
+            try testing.expect(received.from.?.ip6.port != 0);
+
+            const onClose = (struct {
+                fn callback(_: ?*void, _: *xev.Loop, _: *xev.Completion, _: Impl, r: xev.CloseError!void) xev.CallbackAction {
+                    _ = r catch unreachable;
+                    return .disarm;
+                }
+            }).callback;
+            server.close(&loop, &c_read, void, null, onClose);
+            client.close(&loop, &c_write, void, null, onClose);
+            try loop.run(.until_done);
+        }
+
         test "UDP: read/write" {
             if (builtin.os.tag == .freebsd) return error.SkipZigTest;
             const testing = std.testing;