diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c57a2903e..4dada1a99 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -93,6 +93,10 @@ New protocols can go either in `scapy/layers` or to
 on common networks, while protocols in `scapy/contrib` should be
 uncommon or specific.
 
+To be precise, `scapy/layers` protocols should not be importing `scapy/contrib`
+protocols, whereas `scapy/contrib` protocols may import both `scapy/contrib` and
+`scapy/layers` protocols.
+
 ### Features
 
 Protocol-related features should be implemented within the same module