diff --git a/libs/surfaces/us2400/strip.cc b/libs/surfaces/us2400/strip.cc
index 6be3e42ef2..89925a2222 100644
--- a/libs/surfaces/us2400/strip.cc
+++ b/libs/surfaces/us2400/strip.cc
@@ -592,15 +592,7 @@ Strip::handle_pot (Pot& pot, float delta)
 		}
 
 	} else {
-
-		double p = ac->get_interface();
-
-		p += delta;
-
-		p = max (0.0, p);
-		p = min (1.0, p);
-
-		ac->set_value ( ac->interface_to_internal(p), gcd);
+		ac->set_interface ((ac->internal_to_interface (ac->get_value(), true) + delta), true, gcd);
 	}
 }
 
diff --git a/libs/surfaces/us2400/surface.cc b/libs/surfaces/us2400/surface.cc
index 2726851539..7ca3e03233 100644
--- a/libs/surfaces/us2400/surface.cc
+++ b/libs/surfaces/us2400/surface.cc
@@ -643,13 +643,11 @@ Surface::handle_midi_controller_message (MIDI::Parser &, MIDI::EventTwoBytes* ev
 			if (r && r->is_input_strip()) {
 				boost::shared_ptr<AutomationControl> pc = r->send_pan_azimuth_controllable (10);
 				if (pc) {
-					float v = pc->interface_to_internal(value);
-					pc->set_value (v, PBD::Controllable::NoGroup);
+					pc->set_interface (value, true);
 				}
 				pc = r->send_pan_azimuth_controllable (11);
 				if (pc) {
-					float v = pc->interface_to_internal(value);
-					pc->set_value (v, PBD::Controllable::NoGroup);
+					pc->set_interface (value, true);
 				}
 			}
 		}