diff --git a/src/internet/model/tcp-option-sack.cc b/src/internet/model/tcp-option-sack.cc
index cb8abfee2..58120fe29 100644
--- a/src/internet/model/tcp-option-sack.cc
+++ b/src/internet/model/tcp-option-sack.cc
@@ -156,4 +156,13 @@ TcpOptionSack::GetSackList (void) const
   return m_sackList;
 }
 
+std::ostream &
+operator<< (std::ostream & os, TcpOptionSack::SackBlock const & sackBlock)
+{
+  std::stringstream ss;
+  ss << "[" << sackBlock.first << ";" << sackBlock.second << "]";
+  os << ss.str ();
+  return os;
+}
+
 } // namespace ns3
diff --git a/src/internet/model/tcp-option-sack.h b/src/internet/model/tcp-option-sack.h
index d33eb6eca..18d20f78f 100644
--- a/src/internet/model/tcp-option-sack.h
+++ b/src/internet/model/tcp-option-sack.h
@@ -96,6 +96,15 @@ protected:
   SackList m_sackList; //!< the list of SACK blocks
 };
 
+/**
+ * \brief Output operator.
+ * \param os The output stream.
+ * \param sackBlock the block to print.
+ * \returns The output stream.
+ */
+std::ostream & operator<< (std::ostream & os,
+                           TcpOptionSack::SackBlock const & sackBlock);
+
 } // namespace ns3
 
 #endif /* TCP_OPTION_SACK */