diff --git a/README.md b/README.md
index 4ad8d5d..e3c3d64 100644
--- a/README.md
+++ b/README.md
@@ -138,3 +138,8 @@ try "-l 4K".
 * On OpenBSD, the server seems to require a "-4" argument, implying
 that it can only be used with IPv4.
 
+* When specifying the TCP buffer size using the "-w" flag on Linux, Linux 
+doubles the value you pass in. (You can see this using iperf3's debug flag). 
+But then the CWND does not actually ramp up to the doubled value, but only
+to about 75% of the doubled value. This appears to be by design.
+