diff --git a/ipc/chromium/src/third_party/libevent/README.mozilla b/ipc/chromium/src/third_party/libevent/README.mozilla
--- a/ipc/chromium/src/third_party/libevent/README.mozilla
+++ b/ipc/chromium/src/third_party/libevent/README.mozilla
@@ -20,8 +20,12 @@
 Mac doesn't need this since only 64-bit is supported. Use __LP64__ to
 distinguish the two cases. If you get something wrong, the CHECK_EVENT_SIZEOF
 static assertions in message_pump_libevent.cc will fail. If a new constant is
 added, also add a static assertion for it to message_pump_libevent.cc.
 
+You also need to modify the EVENT__HAVE_ARC4RANDOM and EVENT__HAVE_ARC4RANDOM_BUF
+constants in the generated Linux header to account for the results of the arc4random
+and arc4random_buf configure checks.
+
 2. No additional patches are needed at this time, but be careful to avoid
 clobbering changes to the various event-config.h files which have been customized
 over time to avoid various build bustages.
diff --git a/ipc/chromium/src/third_party/libevent/linux/event2/event-config.h b/ipc/chromium/src/third_party/libevent/linux/event2/event-config.h
--- a/ipc/chromium/src/third_party/libevent/linux/event2/event-config.h
+++ b/ipc/chromium/src/third_party/libevent/linux/event2/event-config.h
@@ -27,18 +27,22 @@
 #define EVENT__HAVE_ACCEPT4 1
 
 /* Define to 1 if you have the <afunix.h> header file. */
 /* #undef EVENT__HAVE_AFUNIX_H 1 */
 
+#ifdef HAVE_ARC4RANDOM
 /* Define to 1 if you have the `arc4random' function. */
-/* #undef EVENT__HAVE_ARC4RANDOM */
+#define EVENT__HAVE_ARC4RANDOM 1
+#endif
 
 /* Define to 1 if you have the `arc4random_addrandom' function. */
 /* #undef EVENT__HAVE_ARC4RANDOM_ADDRANDOM */
 
+#ifdef HAVE_ARC4RANDOM_BUF
 /* Define to 1 if you have the `arc4random_buf' function. */
-/* #undef EVENT__HAVE_ARC4RANDOM_BUF */
+#define EVENT__HAVE_ARC4RANDOM_BUF 1
+#endif
 
 /* Define to 1 if you have the <arpa/inet.h> header file. */
 #define EVENT__HAVE_ARPA_INET_H 1
 
 /* Define to 1 if you have the `clock_gettime' function. */