diff --git a/crates/ruma-events/src/room.rs b/crates/ruma-events/src/room.rs
index 41466973..fa6fe087 100644
--- a/crates/ruma-events/src/room.rs
+++ b/crates/ruma-events/src/room.rs
@@ -6,7 +6,7 @@ use std::collections::BTreeMap;
 
 use js_int::UInt;
 use ruma_identifiers::MxcUri;
-use ruma_serde::Base64;
+use ruma_serde::{base64::UrlSafe, Base64};
 use serde::{Deserialize, Serialize};
 
 pub mod aliases;
@@ -193,7 +193,7 @@ pub struct JsonWebKey {
     pub alg: String,
 
     /// The key, encoded as url-safe unpadded base64.
-    pub k: Base64,
+    pub k: Base64<UrlSafe>,
 
     /// Extractable.
     ///
@@ -225,7 +225,7 @@ pub struct JsonWebKeyInit {
     pub alg: String,
 
     /// The key, encoded as url-safe unpadded base64.
-    pub k: Base64,
+    pub k: Base64<UrlSafe>,
 
     /// Extractable.
     ///
diff --git a/crates/ruma-serde/src/base64.rs b/crates/ruma-serde/src/base64.rs
index 1ab0b1ab..bf13387a 100644
--- a/crates/ruma-serde/src/base64.rs
+++ b/crates/ruma-serde/src/base64.rs
@@ -2,15 +2,39 @@ use std::fmt;
 
 use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
 
-/// DOCS
-// generic?
+/// A wrapper around `B` (usually `Vec<u8>`) that (de)serializes from / to a base64 string.
+///
+/// The base64 character set (and miscellaneous other encoding / decoding options) can be customized
+/// through the generic parameter `C`.
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
-pub struct Base64<B = Vec<u8>> {
+pub struct Base64<C = Standard, B = Vec<u8>> {
     bytes: B,
 }
 
-// See https://github.com/matrix-org/matrix-doc/issues/3211
-const BASE64_CONFIG: base64::Config = base64::STANDARD_NO_PAD.decode_allow_trailing_bits(true);
+pub trait Base64Config {
+    const CONF: base64::Config;
+}
+
+/// Standard base64 character set without padding.
+///
+/// Allows trailing bits in decoding for maximum compatibility.
+#[non_exhaustive]
+pub struct Standard;
+
+impl Base64Config for Standard {
+    // See https://github.com/matrix-org/matrix-doc/issues/3211
+    const CONF: base64::Config = base64::STANDARD_NO_PAD.decode_allow_trailing_bits(true);
+}
+
+/// Url-safe base64 character set without padding.
+///
+/// Allows trailing bits in decoding for maximum compatibility.
+#[non_exhaustive]
+pub struct UrlSafe;
+
+impl Base64Config for UrlSafe {
+    const CONF: base64::Config = base64::URL_SAFE_NO_PAD.decode_allow_trailing_bits(true);
+}
 
 impl<B: AsRef<[u8]>> Base64<B> {
     /// Create a `Base64` instance from raw bytes, to be base64-encoded in serialialization.
diff --git a/crates/ruma-serde/src/lib.rs b/crates/ruma-serde/src/lib.rs
index 759f7f40..f7081ea5 100644
--- a/crates/ruma-serde/src/lib.rs
+++ b/crates/ruma-serde/src/lib.rs
@@ -6,7 +6,7 @@
 
 use serde_json::Value as JsonValue;
 
-mod base64;
+pub mod base64;
 mod buf;
 pub mod can_be_empty;
 mod canonical_json;