diff --git a/bufferevent-internal.h b/bufferevent-internal.h
index f369659ffa..b1026f6813 100644
--- a/bufferevent-internal.h
+++ b/bufferevent-internal.h
@@ -33,6 +33,8 @@ extern "C" {
 #include "event-config.h"
 #include "evutil.h"
 #include "defer-internal.h"
+#include "evthread-internal.h"
+#include "event2/thread.h"
 
 struct bufferevent_private {
 	struct bufferevent bev;
@@ -42,6 +44,7 @@ struct bufferevent_private {
 
 	/** If set, read is suspended until evbuffer some. */
 	unsigned read_suspended : 1;
+	unsigned own_lock : 1;
 
 	enum bufferevent_options options;
 
@@ -106,6 +109,22 @@ void bufferevent_wm_suspend_read(struct bufferevent *bufev);
  * read buffer is too full. */
 void bufferevent_wm_unsuspend_read(struct bufferevent *bufev);
 
+int bufferevent_enable_locking(struct bufferevent *bufev, void *lock);
+
+#define BEV_UPCAST(b) EVUTIL_UPCAST((b), struct bufferevent_private, bev)
+
+#define BEV_LOCK(b) do {						\
+		struct bufferevent_private *locking =  BEV_UPCAST(b);	\
+		if (locking->lock)					\
+			EVLOCK_LOCK(locking->lock, EVTHREAD_WRITE);	\
+	} while(0)
+
+#define BEV_UNLOCK(b) do {						\
+		struct bufferevent_private *locking =  BEV_UPCAST(b);	\
+		if (locking->lock)					\
+			EVLOCK_UNLOCK(locking->lock, EVTHREAD_WRITE);	\
+	} while(0)
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/bufferevent.c b/bufferevent.c
index 69b8670243..f92a52bcd9 100644
--- a/bufferevent.c
+++ b/bufferevent.c
@@ -59,16 +59,17 @@
 #include "bufferevent-internal.h"
 #include "util-internal.h"
 
-
 void
 bufferevent_wm_suspend_read(struct bufferevent *bufev)
 {
 	struct bufferevent_private *bufev_private =
 	    EVUTIL_UPCAST(bufev, struct bufferevent_private, bev);
+	BEV_LOCK(bufev);
 	if (!bufev_private->read_suspended) {
 		bufev->be_ops->disable(bufev, EV_READ);
 		bufev_private->read_suspended = 1;
 	}
+	BEV_LOCK(bufev);
 }
 
 void
@@ -76,11 +77,14 @@ bufferevent_wm_unsuspend_read(struct bufferevent *bufev)
 {
 	struct bufferevent_private *bufev_private =
 	    EVUTIL_UPCAST(bufev, struct bufferevent_private, bev);
+
+	BEV_LOCK(bufev);
 	if (bufev_private->read_suspended) {
 		bufev_private->read_suspended = 0;
 		if (bufev->enabled & EV_READ)
 			bufev->be_ops->enable(bufev, EV_READ);
 	}
+	BEV_LOCK(bufev);
 }
 
 /* Callback to implement watermarks on the input buffer.  Only enabled
@@ -91,7 +95,9 @@ bufferevent_inbuf_wm_cb(struct evbuffer *buf,
     void *arg)
 {
 	struct bufferevent *bufev = arg;
-        size_t size = evbuffer_get_length(buf);
+        size_t size;
+
+	size = evbuffer_get_length(buf);
 
 	if (cbinfo->n_added > cbinfo->n_deleted) {
 		/* Data got added.  If it put us over the watermark, stop
@@ -137,6 +143,15 @@ bufferevent_init_common(struct bufferevent_private *bufev_private,
 	 */
 	bufev->enabled = EV_WRITE;
 
+#ifndef _EVENT_DISABLE_THREAD_SUPPORT
+	if (options & BEV_OPT_THREADSAFE) {
+		if (bufferevent_enable_locking(bufev, NULL) < 0) {
+			/* cleanup */
+			return -1;
+		}
+	}
+#endif
+
 	bufev_private->options = options;
 
 	return 0;
@@ -146,11 +161,14 @@ void
 bufferevent_setcb(struct bufferevent *bufev,
     evbuffercb readcb, evbuffercb writecb, everrorcb errorcb, void *cbarg)
 {
+	BEV_LOCK(bufev);
+
 	bufev->readcb = readcb;
 	bufev->writecb = writecb;
 	bufev->errorcb = errorcb;
 
 	bufev->cbarg = cbarg;
+	BEV_UNLOCK(bufev);
 }
 
 struct evbuffer *
@@ -206,15 +224,19 @@ bufferevent_enable(struct bufferevent *bufev, short event)
 	struct bufferevent_private *bufev_private =
 	    EVUTIL_UPCAST(bufev, struct bufferevent_private, bev);
 	short impl_events = event;
+	int r = 0;
+
+	BEV_LOCK(bufev);
 	if (bufev_private->read_suspended)
 		impl_events &= ~EV_READ;
 
 	bufev->enabled |= event;
 
 	if (bufev->be_ops->enable(bufev, impl_events) < 0)
-		return -1;
+		r = -1;
 
-	return (0);
+	BEV_UNLOCK(bufev);
+	return r;
 }
 
 void
@@ -222,6 +244,7 @@ bufferevent_set_timeouts(struct bufferevent *bufev,
 			 const struct timeval *tv_read,
 			 const struct timeval *tv_write)
 {
+	BEV_LOCK(bufev);
 	if (tv_read) {
 		bufev->timeout_read = *tv_read;
 	} else {
@@ -235,6 +258,7 @@ bufferevent_set_timeouts(struct bufferevent *bufev,
 
 	if (bufev->be_ops->adj_timeouts)
 		bufev->be_ops->adj_timeouts(bufev);
+	BEV_UNLOCK(bufev);
 }
 
 
@@ -265,12 +289,16 @@ bufferevent_settimeout(struct bufferevent *bufev,
 int
 bufferevent_disable(struct bufferevent *bufev, short event)
 {
+	int r = 0;
+
+	BEV_LOCK(bufev);
 	bufev->enabled &= ~event;
 
 	if (bufev->be_ops->disable(bufev, event) < 0)
-		return (-1);
+		r = -1;
 
-	return (0);
+	BEV_UNLOCK(bufev);
+	return r;
 }
 
 /*
@@ -284,6 +312,7 @@ bufferevent_setwatermark(struct bufferevent *bufev, short events,
 	struct bufferevent_private *bufev_private =
 	    EVUTIL_UPCAST(bufev, struct bufferevent_private, bev);
 
+	BEV_LOCK(bufev);
 	if (events & EV_WRITE) {
 		bufev->wm_write.low = lowmark;
 		bufev->wm_write.high = highmark;
@@ -321,6 +350,7 @@ bufferevent_setwatermark(struct bufferevent *bufev, short events,
 			bufferevent_wm_unsuspend_read(bufev);
 		}
 	}
+	BEV_UNLOCK(bufev);
 }
 
 int
@@ -328,10 +358,12 @@ bufferevent_flush(struct bufferevent *bufev,
     short iotype,
     enum bufferevent_flush_mode mode)
 {
+	int r = -1;
+	BEV_LOCK(bufev);
         if (bufev->be_ops->flush)
-                return bufev->be_ops->flush(bufev, iotype, mode);
-        else
-                return -1;
+                r = bufev->be_ops->flush(bufev, iotype, mode);
+	BEV_UNLOCK(bufev);
+	return r;
 }
 
 void
@@ -347,5 +379,32 @@ bufferevent_free(struct bufferevent *bufev)
 
 	/* Free the actual allocated memory. */
 	mm_free(bufev - bufev->be_ops->mem_offset);
+	/* Free lock XXX */
+}
+
+int
+bufferevent_enable_locking(struct bufferevent *bufev, void *lock)
+{
+#ifdef _EVENT_DISABLE_THREAD_SUPPORT
+	return -1;
+#else
+	if (BEV_UPCAST(bufev)->lock)
+		return -1;
+
+	if (!lock) {
+		EVTHREAD_ALLOC_LOCK(lock);
+		if (!lock)
+			return -1;
+		BEV_UPCAST(bufev)->lock = lock;
+		BEV_UPCAST(bufev)->own_lock = 1;
+	} else {
+		BEV_UPCAST(bufev)->lock = lock;
+		BEV_UPCAST(bufev)->own_lock = 0;
+	}
+	evbuffer_enable_locking(bufev->input, lock);
+	evbuffer_enable_locking(bufev->output, lock);
+
+	return 0;
+#endif
 }
 
diff --git a/bufferevent_filter.c b/bufferevent_filter.c
index 54fd23c828..b427cfb207 100644
--- a/bufferevent_filter.c
+++ b/bufferevent_filter.c
@@ -170,6 +170,7 @@ bufferevent_filter_new(struct bufferevent *underlying,
 		       void *ctx)
 {
 	struct bufferevent_filtered *bufev_f;
+	enum bufferevent_options tmp_options = options & ~BEV_OPT_THREADSAFE;
 
 	if (!input_filter)
 		input_filter = be_null_filter;
@@ -181,10 +182,18 @@ bufferevent_filter_new(struct bufferevent *underlying,
 		return NULL;
 
 	if (bufferevent_init_common(&bufev_f->bev, underlying->ev_base,
-				    &bufferevent_ops_filter, options) < 0) {
+				    &bufferevent_ops_filter, tmp_options) < 0) {
 		mm_free(bufev_f);
 		return NULL;
 	}
+	if (options & BEV_OPT_THREADSAFE) {
+		void *lock = BEV_UPCAST(underlying)->lock;
+		if (!lock) {
+			bufferevent_enable_locking(underlying, NULL);
+			lock = BEV_UPCAST(underlying)->lock;
+		}
+		bufferevent_enable_locking(downcast(bufev_f), lock);
+	}
 
 	bufev_f->underlying = underlying;
 	bufev_f->process_in = input_filter;
diff --git a/bufferevent_pair.c b/bufferevent_pair.c
index 6fed0e0331..6080421c0c 100644
--- a/bufferevent_pair.c
+++ b/bufferevent_pair.c
@@ -75,6 +75,7 @@ run_callback(struct deferred_cb *cb, void *arg)
 	struct bufferevent_pair *bufev = arg;
 	struct bufferevent *bev = downcast(bufev);
 
+	BEV_LOCK(bev);
 	if (cb == &bufev->deferred_read_cb) {
 		if (bev->readcb) {
 			bev->readcb(bev, bev->cbarg);
@@ -84,6 +85,7 @@ run_callback(struct deferred_cb *cb, void *arg)
 			bev->writecb(bev, bev->cbarg);
 		}
 	}
+	BEV_UNLOCK(bev);
 }
 
 static struct bufferevent_pair *
@@ -115,16 +117,22 @@ bufferevent_pair_new(struct event_base *base, enum bufferevent_options options,
     struct bufferevent *pair[2])
 {
         struct bufferevent_pair *bufev1 = NULL, *bufev2 = NULL;
+	enum bufferevent_options tmp_options = options & ~BEV_OPT_THREADSAFE;
 
 	bufev1 = bufferevent_pair_elt_new(base, options);
 	if (!bufev1)
 		return -1;
-	bufev2 = bufferevent_pair_elt_new(base, options);
+	bufev2 = bufferevent_pair_elt_new(base, tmp_options);
 	if (!bufev2) {
 		bufferevent_free(downcast(bufev1));
 		return -1;
 	}
 
+	if (options & BEV_OPT_THREADSAFE) {
+		/*XXXX check return */
+		bufferevent_enable_locking(downcast(bufev2), bufev1->bev.lock);
+	}
+
 	bufev1->partner = bufev2;
 	bufev2->partner = bufev1;
 
diff --git a/bufferevent_sock.c b/bufferevent_sock.c
index 0e5e3a7b77..5d6b92be27 100644
--- a/bufferevent_sock.c
+++ b/bufferevent_sock.c
@@ -342,6 +342,7 @@ be_socket_flush(struct bufferevent *bev, short iotype,
 void
 bufferevent_setfd(struct bufferevent *bufev, evutil_socket_t fd)
 {
+	BEV_LOCK(bufev);
 	assert(bufev->be_ops == &bufferevent_ops_socket);
 
 	event_del(&bufev->ev_read);
@@ -351,37 +352,48 @@ bufferevent_setfd(struct bufferevent *bufev, evutil_socket_t fd)
 	    EV_READ|EV_PERSIST, bufferevent_readcb, bufev);
 	event_assign(&bufev->ev_write, bufev->ev_base, fd,
 	    EV_WRITE|EV_PERSIST, bufferevent_writecb, bufev);
+	BEV_UNLOCK(bufev);
 }
 
 /* XXXX Should non-socket buffferevents support this? */
 int
 bufferevent_priority_set(struct bufferevent *bufev, int priority)
 {
+	int r = -1;
+
+	BEV_LOCK(bufev);
 	if (bufev->be_ops != &bufferevent_ops_socket)
-		return -1;
+		goto done;
 
 	if (event_priority_set(&bufev->ev_read, priority) == -1)
-		return (-1);
+		goto done;
 	if (event_priority_set(&bufev->ev_write, priority) == -1)
-		return (-1);
+		goto done;
 
-	return (0);
+	r = 0;
+done:
+	BEV_UNLOCK(bufev);
+	return r;
 }
 
 /* XXXX Should non-socket buffferevents support this? */
 int
 bufferevent_base_set(struct event_base *base, struct bufferevent *bufev)
 {
-	int res;
+	int res = -1;
+
+	BEV_LOCK(bufev);
 	if (bufev->be_ops != &bufferevent_ops_socket)
-		return -1;
+		goto done;
 
 	bufev->ev_base = base;
 
 	res = event_base_set(base, &bufev->ev_read);
 	if (res == -1)
-		return (res);
+		goto done;
 
 	res = event_base_set(base, &bufev->ev_write);
-	return (res);
+done:
+	BEV_UNLOCK(bufev);
+	return res;
 }
diff --git a/include/event2/bufferevent.h b/include/event2/bufferevent.h
index bbb70ad86d..41f976b68d 100644
--- a/include/event2/bufferevent.h
+++ b/include/event2/bufferevent.h
@@ -118,6 +118,7 @@ typedef void (*everrorcb)(struct bufferevent *bev, short what, void *ctx);
 
 enum bufferevent_options {
 	BEV_OPT_CLOSE_ON_FREE = (1<<0),
+	BEV_OPT_THREADSAFE = (1<<1),
 };
 
 /**