diff --git a/README.md b/README.md
index 29fa0ed61..5a8a1710d 100644
--- a/README.md
+++ b/README.md
@@ -66,6 +66,19 @@ The following changes are allowed:
 Note that none of the above allowed changes affects the binary wire representation or the
 JSON wire representation.
 
+The following additive changes are allowed:
+
+- Adding new fields to existing messages.
+- Adding new messages or enums.
+- Adding new choices to existing enums.
+- Adding new choices to existing oneof fields.
+- Adding new services.
+- Adding new methods to existing services.
+
+All the additive changes above must be accompanied by an explanation about how
+new and old senders and receivers that implement the version of the protocol
+before and after the change interoperate.
+
 No guarantees are provided whatsoever about the stability of the code that
 is generated from the .proto files by any particular code generator.