diff --git a/doc/assert.txt b/doc/assert.txt
index fd9979032..a2f87b5e8 100644
--- a/doc/assert.txt
+++ b/doc/assert.txt
@@ -44,6 +44,9 @@ including calls, attributes, comparisons, and binary and unary operators. This
 allows you to use the idiomatic python constructs without boilerplate code while
 not losing introspection information.
 
+Assertion introspection is enabled only when a message is not manually provided
+in the assert statement.
+
 See :ref:`assert-details` for more information on assertion introspection.