diff --git a/libs/surfaces/mackie/mcp_buttons.cc b/libs/surfaces/mackie/mcp_buttons.cc
index 83f3d8ebd6..215e547604 100644
--- a/libs/surfaces/mackie/mcp_buttons.cc
+++ b/libs/surfaces/mackie/mcp_buttons.cc
@@ -67,12 +67,14 @@ LedState
 MackieControlProtocol::control_press (Button &)
 {
 	_modifier_state |= MODIFIER_CONTROL;
+	DEBUG_TRACE (DEBUG::MackieControl, string_compose ("CONTROL Press: modifier state now set to %1\n", _modifier_state));
 	return on;
 }
 LedState
 MackieControlProtocol::control_release (Button &)
 {
 	_modifier_state &= ~MODIFIER_CONTROL;
+	DEBUG_TRACE (DEBUG::MackieControl, string_compose ("CONTROL Release: modifier state now set to %1\n", _modifier_state));
 	return on;
 }
 LedState