diff --git a/libs/ardour/ardour/export_format_base.h b/libs/ardour/ardour/export_format_base.h
index c5880aea6b..0ba5f73e8d 100644
--- a/libs/ardour/ardour/export_format_base.h
+++ b/libs/ardour/ardour/export_format_base.h
@@ -146,7 +146,6 @@ class ExportFormatBase {
 	virtual ~ExportFormatBase ();
 
 	boost::shared_ptr<ExportFormatBase> get_intersection (ExportFormatBase const & other) const;
-	boost::shared_ptr<ExportFormatBase> get_difference (ExportFormatBase const & other) const;
 	boost::shared_ptr<ExportFormatBase> get_union (ExportFormatBase const & other) const;
 
 	bool endiannesses_empty () const { return endiannesses.empty (); }
@@ -189,7 +188,6 @@ class ExportFormatBase {
 
 	enum SetOperation {
 		SetUnion,
-		SetDifference,
 		SetIntersection
 	};
 
diff --git a/libs/ardour/export_format_base.cc b/libs/ardour/export_format_base.cc
index 92400b5e47..62fae52c9e 100644
--- a/libs/ardour/export_format_base.cc
+++ b/libs/ardour/export_format_base.cc
@@ -70,12 +70,6 @@ ExportFormatBase::get_intersection (ExportFormatBase const & other) const
 	return do_set_operation (other, SetIntersection);
 }
 
-boost::shared_ptr<ExportFormatBase>
-ExportFormatBase::get_difference (ExportFormatBase const & other) const
-{
-	return do_set_operation (other, SetDifference);
-}
-
 boost::shared_ptr<ExportFormatBase>
 ExportFormatBase::get_union (ExportFormatBase const & other) const
 {
@@ -101,9 +95,6 @@ ExportFormatBase::do_set_operation (ExportFormatBase const & other, SetOperation
 		  case SetIntersection:
 			std::set_intersection (start1, end1, start2, end2, insert);
 			break;
-		  case SetDifference:
-			std::set_difference (start1, end1, start2, end2, insert);
-			break;
 		  case SetUnion:
 			std::set_union (start1, end1, start2, end2, insert);
 			break;
@@ -122,9 +113,6 @@ ExportFormatBase::do_set_operation (ExportFormatBase const & other, SetOperation
 		  case SetIntersection:
 			std::set_intersection (start1, end1, start2, end2, insert);
 			break;
-		  case SetDifference:
-			std::set_difference (start1, end1, start2, end2, insert);
-			break;
 		  case SetUnion:
 			std::set_union (start1, end1, start2, end2, insert);
 			break;
@@ -144,9 +132,6 @@ ExportFormatBase::do_set_operation (ExportFormatBase const & other, SetOperation
 		  case SetIntersection:
 			std::set_intersection (start1, end1, start2, end2, insert);
 			break;
-		  case SetDifference:
-			std::set_difference (start1, end1, start2, end2, insert);
-			break;
 		  case SetUnion:
 			std::set_union (start1, end1, start2, end2, insert);
 			break;
@@ -165,9 +150,6 @@ ExportFormatBase::do_set_operation (ExportFormatBase const & other, SetOperation
 		  case SetIntersection:
 			std::set_intersection (start1, end1, start2, end2, insert);
 			break;
-		  case SetDifference:
-			std::set_difference (start1, end1, start2, end2, insert);
-			break;
 		  case SetUnion:
 			std::set_union (start1, end1, start2, end2, insert);
 			break;
@@ -186,9 +168,6 @@ ExportFormatBase::do_set_operation (ExportFormatBase const & other, SetOperation
 		  case SetIntersection:
 			std::set_intersection (start1, end1, start2, end2, insert);
 			break;
-		  case SetDifference:
-			std::set_difference (start1, end1, start2, end2, insert);
-			break;
 		  case SetUnion:
 			std::set_union (start1, end1, start2, end2, insert);
 			break;