diff --git a/src/mapping/map.rs b/src/mapping/map.rs
index 6b2eabb..49e90ac 100644
--- a/src/mapping/map.rs
+++ b/src/mapping/map.rs
@@ -145,7 +145,10 @@ impl MapFile {
 
             master.domain.end = self.map[idx].domain.end;
             new_map.push(master);
+            idx += 1;
         }
+
+        self.map = new_map;
     }
 
     /// Extend the domain of the MapFile.