diff --git a/src/internet/model/tcp-socket-base.cc b/src/internet/model/tcp-socket-base.cc
index 16058b544..c01a17ab7 100644
--- a/src/internet/model/tcp-socket-base.cc
+++ b/src/internet/model/tcp-socket-base.cc
@@ -677,7 +677,7 @@ TcpSocketBase::DoForwardUp (Ptr<Packet> packet, Ipv4Header header, uint16_t port
   m_rWnd = tcpHeader.GetWindowSize ();
 
   // Discard fully out of range data packets
-  if (packet->GetSize &&
+  if (packet->GetSize () &&
       OutOfRange (tcpHeader.GetSequenceNumber (), tcpHeader.GetSequenceNumber () + packet->GetSize ()))
     {
       NS_LOG_LOGIC ("At state " << TcpStateName[m_state] <<