diff --git a/libs/ardour/plugin_insert.cc b/libs/ardour/plugin_insert.cc
index 13ac7b375a..6fbb5cb679 100644
--- a/libs/ardour/plugin_insert.cc
+++ b/libs/ardour/plugin_insert.cc
@@ -352,6 +352,9 @@ PluginInsert::connect_and_run (BufferSet& bufs, pframes_t nframes, framecnt_t of
 		}
 	}
 
+	bufs.set_count(ChanCount::max(bufs.count(), in_streams));
+	bufs.set_count(ChanCount::max(bufs.count(), out_streams));
+
 	/* Note that we've already required that plugins
 	   be able to handle in-place processing.
 	*/
diff --git a/libs/ardour/port_set.cc b/libs/ardour/port_set.cc
index c7f5e2e674..3489ae4e44 100644
--- a/libs/ardour/port_set.cc
+++ b/libs/ardour/port_set.cc
@@ -145,9 +145,11 @@ PortSet::port(DataType type, size_t n) const
 		return port(n);
 	} else {
 		const PortVec& v = _ports[type];
-		assert(n < v.size());
-		return v[n];
+		if (n < v.size()) {
+			return v[n];
+		}
 	}
+	return boost::shared_ptr<Port>();
 }
 
 boost::shared_ptr<AudioPort>