diff --git a/src/indirect_reference_table.h b/src/indirect_reference_table.h
index b0a0d64..710e43f 100644
--- a/src/indirect_reference_table.h
+++ b/src/indirect_reference_table.h
@@ -287,7 +287,7 @@
 
   void AssertEmpty();
 
-  void Dump() const;
+  void Dump(std::ostream& os) const;
 
   /*
    * Return the #of entries in the entire table.  This includes holes, and