diff --git a/libs/evoral/evoral/Control.h b/libs/evoral/evoral/Control.h
index b0797aeb5f..08f7643f93 100644
--- a/libs/evoral/evoral/Control.h
+++ b/libs/evoral/evoral/Control.h
@@ -35,7 +35,7 @@
 
 namespace Evoral {
 
-class ParameterDescriptor;
+struct ParameterDescriptor;
 class Transport;
 class TypeMap;
 
diff --git a/libs/evoral/evoral/TypeMap.h b/libs/evoral/evoral/TypeMap.h
index af9c8c3962..feb68c5579 100644
--- a/libs/evoral/evoral/TypeMap.h
+++ b/libs/evoral/evoral/TypeMap.h
@@ -29,7 +29,7 @@
 namespace Evoral {
 
 class Parameter;
-class ParameterDescriptor;
+struct ParameterDescriptor;
 
 /** The applications passes one of these which provide the implementation
  * with required information about event types in an opaque, type neutral way
diff --git a/libs/surfaces/mackie/subview.h b/libs/surfaces/mackie/subview.h
index eb744fad86..364d0abb8d 100644
--- a/libs/surfaces/mackie/subview.h
+++ b/libs/surfaces/mackie/subview.h
@@ -25,7 +25,7 @@
 #include "ardour/types.h"
 
 namespace ARDOUR {
-	class ParameterDescriptor;
+	struct ParameterDescriptor;
 	class Plugin;
 	class PluginInsert;
 }
diff --git a/libs/widgets/widgets/pane.h b/libs/widgets/widgets/pane.h
index f092678462..5a46dab759 100644
--- a/libs/widgets/widgets/pane.h
+++ b/libs/widgets/widgets/pane.h
@@ -41,7 +41,7 @@ namespace ArdourWidgets {
 class LIBWIDGETS_API Pane : public Gtk::Container
 {
 private:
-	class Divider;
+	struct Divider;
 
 public:
 	struct Child