diff --git a/src/add-ons/kernel/network/stack/net_buffer.cpp b/src/add-ons/kernel/network/stack/net_buffer.cpp
index 23ccc3d408..da80731deb 100644
--- a/src/add-ons/kernel/network/stack/net_buffer.cpp
+++ b/src/add-ons/kernel/network/stack/net_buffer.cpp
@@ -845,12 +845,15 @@ status_t
 append_cloned_data(net_buffer *_buffer, net_buffer *_source, uint32 offset,
 	size_t bytes)
 {
+	if (bytes == 0)
+		return B_OK;
+
 	net_buffer_private *buffer = (net_buffer_private *)_buffer;
 	net_buffer_private *source = (net_buffer_private *)_source;
 	TRACE(("append_cloned_data(buffer %p, source %p, offset = %ld, bytes = %ld)\n",
 		buffer, source, offset, bytes));
 
-	if (source->size < offset + bytes)
+	if (source->size < offset + bytes || source->size < offset)
 		return B_BAD_VALUE;
 
 	// find data_node to start with from the source buffer
diff --git a/src/add-ons/kernel/network/stack/utility.cpp b/src/add-ons/kernel/network/stack/utility.cpp
index dcc54f2b01..fbb79781e7 100644
--- a/src/add-ons/kernel/network/stack/utility.cpp
+++ b/src/add-ons/kernel/network/stack/utility.cpp
@@ -300,15 +300,18 @@ set_timer(net_timer *timer, bigtime_t delay)
 {
 	BenaphoreLocker locker(sTimerLock);
 
-	if (timer->due > 0) {
-		// this timer is already scheduled, cancel it
+	if (timer->due > 0 && delay < 0) {
+		// this timer is scheduled, cancel it
 		list_remove_item(&sTimers, timer);
+		timer->due = 0;
 	}
 
 	if (delay >= 0) {
-		// add this timer
+		// reschedule or add this timer
+		if (timer->due <= 0)
+			list_add_item(&sTimers, timer);
+
 		timer->due = system_time() + delay;
-		list_add_item(&sTimers, timer);
 
 		// notify timer about the change if necessary
 		if (sTimerTimeout > timer->due)