diff --git a/src/iosource/PktSrc.cc b/src/iosource/PktSrc.cc
index 2ca5d2720e..0fa9585621 100644
--- a/src/iosource/PktSrc.cc
+++ b/src/iosource/PktSrc.cc
@@ -139,6 +139,16 @@ void PktSrc::Done()
 		Close();
 	}
 
+bool PktSrc::HasBeenIdleFor(double interval) const
+	{
+	if ( have_packet || had_packet )
+		return false;
+
+	// Take the hit of a current_time() call now.
+	double now = zeek::util::current_time(true);
+	return idle_at_wallclock < now - interval;
+	};
+
 void PktSrc::Process()
 	{
 	if ( ! IsOpen() )
@@ -191,6 +201,18 @@ bool PktSrc::ExtractNextPacketInternal()
 		}
 	else
 		{
+		// Update the idle_at timestamp the first time we've failed
+		// to extract a packet. This assumes ExtractNextPacket() is
+		// called regularly which is true for non-selectable PktSrc
+		// instances, but even for selectable ones with an FD the
+		// main-loop will call Process() on the interface regularly
+		// and detect it as idle.
+		if ( had_packet )
+			{
+			DBG_LOG(DBG_PKTIO, "source %s is idle now", props.path.c_str());
+			idle_at_wallclock = zeek::util::current_time(true);
+			}
+
 		had_packet = false;
 		}
 
diff --git a/src/iosource/PktSrc.h b/src/iosource/PktSrc.h
index d93b5d60bc..a1ef1c6e64 100644
--- a/src/iosource/PktSrc.h
+++ b/src/iosource/PktSrc.h
@@ -88,6 +88,24 @@ public:
 	 */
 	bool IsError() const;
 
+	/**
+	 * Return true if the source has been observed idle for the given
+	 * wallclock interval.
+	 *
+	 * The default implementation looks at failing ExtractNextPacket() calls
+	 * and keeps the wallclock timestamp when there was no packet available.
+	 * The source is considered idle when there has not been a packet since
+	 * \a interval seconds.
+	 *
+	 * Alternative implementations may check internally buffered packets
+	 * or queue lengths.
+	 *
+	 * @param interval Interval in seconds.
+	 *
+	 * @return True if the source has been idle for \a interval seconds.
+	 */
+	virtual bool HasBeenIdleFor(double interval) const;
+
 	/**
 	 * If the source encountered an error, returns a corresponding error
 	 * message. Returns an empty string otherwise.
@@ -365,6 +383,8 @@ private:
 	// Did the previous call to ExtractNextPacket() yield a packet.
 	bool had_packet;
 
+	double idle_at_wallclock = 0.0;
+
 	// For BPF filtering support.
 	std::vector<detail::BPF_Program*> filters;