diff --git a/src/Interval.cpp b/src/Interval.cpp
index 7ee57e04..bc4355d7 100644
--- a/src/Interval.cpp
+++ b/src/Interval.cpp
@@ -199,6 +199,9 @@ std::string Interval::dump () const
       out << ' ' << quoteIfNeeded (tag);
   }
 
+  if (synthetic)
+    out << " synthetic";
+
   return out.str ();
 }
 
diff --git a/src/Interval.h b/src/Interval.h
index 65f328d3..73a2a0bd 100644
--- a/src/Interval.h
+++ b/src/Interval.h
@@ -48,8 +48,9 @@ public:
   std::string dump () const;
 
 public:
-  Range                  range  {};
-  int                    id     {0};
+  Range                  range     {};
+  int                    id        {0};
+  bool                   synthetic {false};
 
 private:
   std::set <std::string> _tags  {};