diff --git a/libs/pbd/pbd/search_path.h b/libs/pbd/pbd/search_path.h
index 86ab5cdc64..74ac764dc0 100644
--- a/libs/pbd/pbd/search_path.h
+++ b/libs/pbd/pbd/search_path.h
@@ -90,12 +90,12 @@ public:
 	/**
 	 * Concatenate another Searchpath onto this.
 	 */
-	LIBPBD_TEMPLATE_MEMBER_API Searchpath& operator+ (const Searchpath& other);
+	LIBPBD_TEMPLATE_MEMBER_API const Searchpath operator+ (const Searchpath& other);
 	
 	/**
 	 * Add another path to the search path.
 	 */
-	LIBPBD_TEMPLATE_MEMBER_API Searchpath& operator+ (const std::string& directory_path);
+	LIBPBD_TEMPLATE_MEMBER_API const Searchpath operator+ (const std::string& directory_path);
 
 	/**
 	 * Remove all the directories in path from this.
diff --git a/libs/pbd/search_path.cc b/libs/pbd/search_path.cc
index 44438cc85c..1d931a546d 100644
--- a/libs/pbd/search_path.cc
+++ b/libs/pbd/search_path.cc
@@ -124,19 +124,16 @@ Searchpath::operator+= (const std::string& directory_path)
 	return *this;
 }
 
-Searchpath&
+const Searchpath
 Searchpath::operator+ (const std::string& directory_path)
 {
-	add_directory (directory_path);
-	return *this;
+	return Searchpath (*this) += directory_path;
 }
 
-Searchpath&
+const Searchpath
 Searchpath::operator+ (const Searchpath& spath)
 {
-	// concatenate paths into new Searchpath
-	insert(end(), spath.begin(), spath.end());
-	return *this;
+	return Searchpath (*this) += spath;
 }
 
 Searchpath&