diff --git a/crates/ruma-serde/src/base64.rs b/crates/ruma-serde/src/base64.rs
index bf13387a..d6ec03f3 100644
--- a/crates/ruma-serde/src/base64.rs
+++ b/crates/ruma-serde/src/base64.rs
@@ -1,4 +1,6 @@
-use std::fmt;
+//!Transparent base64 encoding / decoding as part of (de)serialization.
+
+use std::{fmt, marker::PhantomData};
 
 use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
 
@@ -9,37 +11,50 @@ use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Base64<C = Standard, B = Vec<u8>> {
     bytes: B,
+    _phantom_conf: PhantomData<*mut C>,
 }
 
+/// Config used for the [`Base64`] type.
 pub trait Base64Config {
-    const CONF: base64::Config;
+    /// The config as a constant.
+    ///
+    /// Opaque so our interface is not tied to the base64 crate version.
+    #[doc(hidden)]
+    const CONF: Conf;
 }
 
+#[doc(hidden)]
+pub struct Conf(base64::Config);
+
 /// Standard base64 character set without padding.
 ///
 /// Allows trailing bits in decoding for maximum compatibility.
 #[non_exhaustive]
+// Easier than implementing these all for Base64 manually to avoid the `C: Trait` bounds.
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
 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);
+    const CONF: Conf = Conf(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]
+// Easier than implementing these all for Base64 manually to avoid the `C: Trait` bounds.
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct UrlSafe;
 
 impl Base64Config for UrlSafe {
-    const CONF: base64::Config = base64::URL_SAFE_NO_PAD.decode_allow_trailing_bits(true);
+    const CONF: Conf = Conf(base64::URL_SAFE_NO_PAD.decode_allow_trailing_bits(true));
 }
 
-impl<B: AsRef<[u8]>> Base64<B> {
+impl<C: Base64Config, B: AsRef<[u8]>> Base64<C, B> {
     /// Create a `Base64` instance from raw bytes, to be base64-encoded in serialialization.
     pub fn new(bytes: B) -> Self {
-        Self { bytes }
+        Self { bytes, _phantom_conf: PhantomData }
     }
 
     /// Get a reference to the raw bytes held by this `Base64` instance.
@@ -49,42 +64,42 @@ impl<B: AsRef<[u8]>> Base64<B> {
 
     /// Encode the bytes contained in this `Base64` instance to unpadded base64.
     pub fn encode(&self) -> String {
-        base64::encode_config(&self.bytes, BASE64_CONFIG)
+        base64::encode_config(&self.bytes, C::CONF.0)
     }
 }
 
-impl<B> Base64<B> {
+impl<C, B> Base64<C, B> {
     /// Get the raw bytes held by this `Base64` instance.
     pub fn into_inner(self) -> B {
         self.bytes
     }
 }
 
-impl Base64 {
+impl<C: Base64Config> Base64<C> {
     /// Create a `Base64` instance containing an empty `Vec<u8>`.
     pub fn empty() -> Self {
-        Self { bytes: Vec::new() }
+        Self::new(Vec::new())
     }
 
     /// Parse some base64-encoded data to create a `Base64` instance.
     pub fn parse(encoded: impl AsRef<[u8]>) -> Result<Self, base64::DecodeError> {
-        base64::decode_config(encoded, BASE64_CONFIG).map(Self::new)
+        base64::decode_config(encoded, C::CONF.0).map(Self::new)
     }
 }
 
-impl<B: AsRef<[u8]>> fmt::Debug for Base64<B> {
+impl<C: Base64Config, B: AsRef<[u8]>> fmt::Debug for Base64<C, B> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.encode().fmt(f)
     }
 }
 
-impl<B: AsRef<[u8]>> fmt::Display for Base64<B> {
+impl<C: Base64Config, B: AsRef<[u8]>> fmt::Display for Base64<C, B> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.encode().fmt(f)
     }
 }
 
-impl<'de> Deserialize<'de> for Base64 {
+impl<'de, C: Base64Config> Deserialize<'de> for Base64<C> {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
@@ -94,7 +109,7 @@ impl<'de> Deserialize<'de> for Base64 {
     }
 }
 
-impl<B: AsRef<[u8]>> Serialize for Base64<B> {
+impl<C: Base64Config, B: AsRef<[u8]>> Serialize for Base64<C, B> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: Serializer,
diff --git a/crates/ruma-signatures/src/functions.rs b/crates/ruma-signatures/src/functions.rs
index c43bc058..4a12d259 100644
--- a/crates/ruma-signatures/src/functions.rs
+++ b/crates/ruma-signatures/src/functions.rs
@@ -9,7 +9,7 @@ use std::{
 
 use base64::{encode_config, STANDARD_NO_PAD, URL_SAFE_NO_PAD};
 use ruma_identifiers::{EventId, RoomVersionId, ServerName, UserId};
-use ruma_serde::{Base64, CanonicalJsonObject, CanonicalJsonValue};
+use ruma_serde::{base64::Standard, Base64, CanonicalJsonObject, CanonicalJsonValue};
 use serde_json::{from_str as from_json_str, to_string as to_json_string};
 use sha2::{digest::Digest, Sha256};
 
@@ -291,7 +291,7 @@ pub fn verify_json(
                 )
             })?;
 
-            let signature = Base64::parse(signature)
+            let signature = Base64::<Standard>::parse(signature)
                 .map_err(|e| ParseError::base64("signature", signature, e))?;
 
             verify_json_with(
@@ -332,8 +332,6 @@ where
 
 /// Creates a *content hash* for an event.
 ///
-/// 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.
 ///
@@ -344,7 +342,7 @@ where
 /// # Errors
 ///
 /// Returns an error if the event is too large.
-pub fn content_hash(object: &CanonicalJsonObject) -> Result<Base64<[u8; 32]>, Error> {
+pub fn content_hash(object: &CanonicalJsonObject) -> Result<Base64<Standard, [u8; 32]>, Error> {
     let json = canonical_json_with_fields_to_remove(object, CONTENT_HASH_FIELDS_TO_REMOVE)?;
     if json.len() > MAX_PDU_BYTES {
         return Err(Error::PduSize);
@@ -656,8 +654,8 @@ pub fn verify_event(
 
         let public_key = signature_and_pubkey.public_key;
 
-        let signature =
-            Base64::parse(signature).map_err(|e| ParseError::base64("signature", signature, e))?;
+        let signature = Base64::<Standard>::parse(signature)
+            .map_err(|e| ParseError::base64("signature", signature, e))?;
 
         verify_json_with(
             &Ed25519Verifier,
@@ -669,7 +667,7 @@ pub fn verify_event(
 
     let calculated_hash = content_hash(object)?;
 
-    if let Ok(hash) = Base64::parse(hash) {
+    if let Ok(hash) = Base64::<Standard>::parse(hash) {
         if hash.as_bytes() == calculated_hash.as_bytes() {
             return Ok(Verified::All);
         }