Updated documentation for removal of bigfile/VARBLOCK support.
diff --git a/doc/compatibility.rst b/doc/compatibility.rst
index aedfcb6..d6e1dc4 100644
--- a/doc/compatibility.rst
+++ b/doc/compatibility.rst
@@ -25,7 +25,8 @@
     PKCS#1 v1.5 in PEM and DER format, ASN.1 type RSAPublicKey
 
 :ref:`VARBLOCK <bigfiles>` encryption:
-    Python-RSA only, not compatible with any other known application.
+    Deprecated in Python-RSA 3.4 and removed from Python-RSA 4.0.
+    Was Python-RSA only, not compatible with any other known application.
 
 .. _openssl:
 
@@ -59,4 +60,3 @@
     openssl rsa -in privatekey-pkcs8.pem -out privatekey.pem
 
 You can then extract the corresponding public key as described above.
-