diff --git a/libc/include/sys/epoll.h b/libc/include/sys/epoll.h
index c06a081..4a5a37c 100644
--- a/libc/include/sys/epoll.h
+++ b/libc/include/sys/epoll.h
@@ -67,7 +67,11 @@
 struct epoll_event {
   uint32_t events;
   epoll_data_t data;
-};
+}
+#ifdef __x86_64__
+__packed
+#endif
+;
 
 int epoll_create(int);
 int epoll_create1(int);
diff --git a/tests/sys_epoll_test.cpp b/tests/sys_epoll_test.cpp
index daa064a..6e7a807 100644
--- a/tests/sys_epoll_test.cpp
+++ b/tests/sys_epoll_test.cpp
@@ -17,8 +17,10 @@
 #include <gtest/gtest.h>
 
 #include <errno.h>
+#include <fcntl.h>
 #include <signal.h>
 #include <sys/epoll.h>
+#include <unistd.h>
 
 TEST(sys_epoll, smoke) {
   int epoll_fd = epoll_create(1);
@@ -37,3 +39,30 @@
   sigaddset(&ss, SIGPIPE);
   ASSERT_EQ(0, epoll_pwait(epoll_fd, events, 1, 1, &ss));
 }
+
+TEST(sys_epoll, epoll_event_data) {
+  int epoll_fd = epoll_create(1);
+  ASSERT_NE(-1, epoll_fd) << strerror(errno);
+
+  int fds[2];
+  ASSERT_NE(-1, pipe(fds));
+
+  const uint64_t expected = 0x123456789abcdef0;
+
+  // Get ready to poll on read end of pipe.
+  epoll_event ev;
+  ev.events = EPOLLIN;
+  ev.data.u64 = expected;
+  ASSERT_NE(-1, epoll_ctl(epoll_fd, EPOLL_CTL_ADD, fds[0], &ev));
+
+  // Ensure there's something in the pipe.
+  ASSERT_EQ(1, write(fds[1], "\n", 1));
+
+  // Poll.
+  epoll_event events[1];
+  ASSERT_EQ(1, epoll_wait(epoll_fd, events, 1, 1));
+  ASSERT_EQ(expected, events[0].data.u64);
+
+  close(fds[0]);
+  close(fds[1]);
+}