diff --git a/src/functions.rs b/src/functions.rs
index dc2aaf2f..f6401697 100644
--- a/src/functions.rs
+++ b/src/functions.rs
@@ -160,7 +160,7 @@ where
 
 /// Creates a *content hash* for the JSON representation of an event.
 ///
-/// Returns the hash as a Base64-encoded string without padding.
+/// Returns the hash as a Base64-encoded string, using the standard character set, without padding.
 ///
 /// The content hash of an event covers the complete event including the unredacted contents. It is
 /// used during federation and is described in the Matrix server-server specification.
@@ -182,7 +182,7 @@ pub fn content_hash(value: &Value) -> Result<String, Error> {
 
 /// Creates a *reference hash* for the JSON representation of an event.
 ///
-/// Returns the hash as a Base64-encoded string without padding.
+/// Returns the hash as a Base64-encoded string, using the standard character set, without padding.
 ///
 /// The reference hash of an event covers the essential fields of an event, including content
 /// hashes. It is used to generate event identifiers and is described in the Matrix server-server
diff --git a/src/lib.rs b/src/lib.rs
index 0e57a544..28d506f3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -11,6 +11,9 @@
 //! algorithm it uses and a "version" string, separated by a colon. The version is an arbitrary
 //! identifier used to distinguish key pairs using the same algorithm from the same homeserver.
 //!
+//! In JSON representations, signatures and hashes appear as Base64-encoded strings, using the
+//! standard character set, without padding.
+//!
 //! # Signing JSON
 //!
 //! A homeserver signs JSON with a key pair: