diff --git a/include/net/tcp.h b/include/net/tcp.h
index 75a00c8..0bdc3f6 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1386,6 +1386,14 @@
 		tcp_sk(sk)->highest_sack = new;
 }
 
+/* Determines whether this is a thin stream (which may suffer from
+ * increased latency). Used to trigger latency-reducing mechanisms.
+ */
+static inline unsigned int tcp_stream_is_thin(struct tcp_sock *tp)
+{
+	return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
+}
+
 /* /proc */
 enum tcp_seq_states {
 	TCP_SEQ_STATE_LISTENING,