diff --git a/README.md b/README.md
index 51aeb4e..941a557 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,7 @@ Some notes about how to make the diagram:
 * You don't need to include a Trust Boundary - it won't get parsed and has no bearing on the threats which appear
 * You don't need to include the STRIDE labels - we generate the threats for you!
 * Bi-directional flows are currently not supported - flows move in one direction. In some cases, data might flow from Entity A to Entity B, while data also flows from Entity B to Entity A; model these as two separate flows and you'll be fine.
+* The direction of a flow is dictated by which element was selected as the source of the flow during flow creation (ie which element the flow was dragged from first). The actual location of the arrowhead does not matter. 
 * Entities must talk to other entities through processes - the process is mandatory and must be included.
 
 ### Example