diff --git a/src/internet/model/tcp-cubic.cc b/src/internet/model/tcp-cubic.cc
index a0281da46..e98af4c1f 100644
--- a/src/internet/model/tcp-cubic.cc
+++ b/src/internet/model/tcp-cubic.cc
@@ -397,7 +397,7 @@ TcpCubic::GetSsThresh (Ptr<const TcpSocketState> tcb, uint32_t bytesInFlight)
   /* Wmax and fast convergence */
   if (segCwnd < m_lastMaxCwnd && m_fastConvergence)
     {
-      m_lastMaxCwnd = m_beta * segCwnd;
+      m_lastMaxCwnd = (segCwnd * (1 + m_beta)) / 2; // Section 4.6 in RFC 8312
     }
   else
     {