diff --git a/libs/ardour/luabindings.cc b/libs/ardour/luabindings.cc
index 3a1c031e9b..fb580b267f 100644
--- a/libs/ardour/luabindings.cc
+++ b/libs/ardour/luabindings.cc
@@ -144,7 +144,7 @@ namespace Cairo {
 CLASSKEYS(Cairo::Context);
 CLASSKEYS(std::vector<double>);
 CLASSKEYS(std::list<ArdourMarker*>);
-CLASSKEYS(std::bitset<47ul>); // LuaSignal::LAST_SIGNAL
+CLASSKEYS(std::bitset<45ul>); // LuaSignal::LAST_SIGNAL
 CLASSKEYS(ArdourMarker*);
 CLASSKEYS(ARDOUR::RouteGroup);
 CLASSKEYS(ARDOUR::LuaProc);