diff --git a/libs/ardour/ardour/monitor_processor.h b/libs/ardour/ardour/monitor_processor.h
index c85b557f6e..e58e8f0a5d 100644
--- a/libs/ardour/ardour/monitor_processor.h
+++ b/libs/ardour/ardour/monitor_processor.h
@@ -119,6 +119,8 @@ protected:
 	T _normal;
 };
 
+template<> void MPControl<bool>::set_value (double v, PBD::Controllable::GroupControlDisposition gcd);
+
 class LIBARDOUR_API MonitorProcessor : public Processor
 {
 public:
diff --git a/libs/ardour/ardour/surround_return.h b/libs/ardour/ardour/surround_return.h
index 5d5e0f3ef8..31672f1af1 100644
--- a/libs/ardour/ardour/surround_return.h
+++ b/libs/ardour/ardour/surround_return.h
@@ -102,17 +102,8 @@ private:
 	class OutputFormatControl : public MPControl<bool>
 	{
 	public:
-		OutputFormatControl (bool v, std::string const& n, PBD::Controllable::Flag f)
-			: MPControl<bool> (v, n, f)
-		{}
-
-		virtual std::string get_user_string () const {
-			if (get_value () == 0) {
-				return "7.1.4";
-			} else {
-				return "5.1";
-			}
-		}
+		OutputFormatControl (bool v, std::string const& n, PBD::Controllable::Flag f);
+		virtual std::string get_user_string () const;
 	};
 
 	std::shared_ptr<OutputFormatControl> _output_format_control;
diff --git a/libs/ardour/surround_return.cc b/libs/ardour/surround_return.cc
index b975dad862..a41c175934 100644
--- a/libs/ardour/surround_return.cc
+++ b/libs/ardour/surround_return.cc
@@ -30,6 +30,19 @@
 
 using namespace ARDOUR;
 
+SurroundReturn::OutputFormatControl::OutputFormatControl (bool v, std::string const& n, PBD::Controllable::Flag f)
+	: MPControl<bool> (v, n, f)
+{}
+
+std::string
+SurroundReturn::OutputFormatControl::get_user_string () const {
+	if (get_value () == 0) {
+		return "7.1.4";
+	} else {
+		return "5.1";
+	}
+}
+
 SurroundReturn::SurroundReturn (Session& s, Route* r)
 	: Processor (s, _("SurrReturn"), Temporal::TimeDomainProvider (Temporal::AudioTime))
 	, _lufs_meter (s.nominal_sample_rate (), 5)