diff --git a/gtk2_ardour/editor.cc b/gtk2_ardour/editor.cc
index c118a2ee76..9a24be433a 100644
--- a/gtk2_ardour/editor.cc
+++ b/gtk2_ardour/editor.cc
@@ -2243,6 +2243,9 @@ Editor::set_state (const XMLNode& node, int /*version*/)
 	if ((prop = node.property ("left-frame")) != 0) {
 		framepos_t pos;
 		if (sscanf (prop->value().c_str(), "%" PRId64, &pos) == 1) {
+			if (pos < 0) {
+				pos = 0;
+			}
 			reset_x_origin (pos);
 		}
 	}
@@ -4308,6 +4311,7 @@ Editor::idle_visual_changer ()
 		*/
 
 		leftmost_frame = pending_visual_change.time_origin;
+		assert (leftmost_frame >= 0);
 	}
 
 	if (p & VisualChange::ZoomLevel) {
diff --git a/gtk2_ardour/editor_ops.cc b/gtk2_ardour/editor_ops.cc
index 96ae169aed..1dd5256d2a 100644
--- a/gtk2_ardour/editor_ops.cc
+++ b/gtk2_ardour/editor_ops.cc
@@ -1581,6 +1581,10 @@ Editor::temporal_zoom_by_frame (framepos_t start, framepos_t end, const string &
 		new_leftmost = 0;
 	}
 
+	if (new_leftmost < 0) {
+		new_leftmost = 0;
+	}
+
 	reposition_and_zoom (new_leftmost, new_fpu);
 }