diff --git a/matrix_sdk_base/src/client.rs b/matrix_sdk_base/src/client.rs
index 59f9b24c..21168bf0 100644
--- a/matrix_sdk_base/src/client.rs
+++ b/matrix_sdk_base/src/client.rs
@@ -1288,9 +1288,9 @@ impl BaseClient {
     #[cfg_attr(docsrs, doc(cfg(feature = "encryption")))]
     pub async fn share_group_session(&self, room_id: &RoomId) -> Result<Vec<OwnedToDeviceRequest>> {
         let room = self.get_joined_room(room_id).await.expect("No room found");
-        let mut olm = self.olm.lock().await;
+        let olm = self.olm.lock().await;
 
-        match &mut *olm {
+        match &*olm {
             Some(o) => {
                 let room = room.write().await;
 
@@ -1417,9 +1417,9 @@ impl BaseClient {
     #[cfg(feature = "encryption")]
     #[cfg_attr(docsrs, doc(cfg(feature = "encryption")))]
     pub async fn invalidate_group_session(&self, room_id: &RoomId) -> bool {
-        let mut olm = self.olm.lock().await;
+        let olm = self.olm.lock().await;
 
-        match &mut *olm {
+        match &*olm {
             Some(o) => o.invalidate_group_session(room_id),
             None => false,
         }
diff --git a/matrix_sdk_crypto/src/machine.rs b/matrix_sdk_crypto/src/machine.rs
index b06ee92e..340af00f 100644
--- a/matrix_sdk_crypto/src/machine.rs
+++ b/matrix_sdk_crypto/src/machine.rs
@@ -15,13 +15,15 @@
 #[cfg(feature = "sqlite-cryptostore")]
 use std::path::Path;
 use std::{
-    collections::{BTreeMap, HashMap, HashSet},
+    collections::{BTreeMap, HashSet},
     convert::{TryFrom, TryInto},
     mem,
     result::Result as StdResult,
     sync::Arc,
 };
 
+use dashmap::DashMap;
+
 use api::r0::{
     keys::{claim_keys, get_keys, upload_keys, DeviceKeys, OneTimeKey},
     sync::sync_events::Response as SyncResponse,
@@ -67,6 +69,7 @@ pub type OneTimeKeys = BTreeMap<DeviceKeyId, OneTimeKey>;
 
 /// State machine implementation of the Olm/Megolm encryption protocol used for
 /// Matrix end to end encryption.
+#[derive(Clone)]
 pub struct OlmMachine {
     /// The unique user id that owns this account.
     user_id: UserId,
@@ -79,7 +82,7 @@ pub struct OlmMachine {
     /// without the need to create new keys.
     store: Arc<RwLock<Box<dyn CryptoStore>>>,
     /// The currently active outbound group sessions.
-    outbound_group_sessions: HashMap<RoomId, OutboundGroupSession>,
+    outbound_group_sessions: Arc<DashMap<RoomId, OutboundGroupSession>>,
     /// A state machine that is responsible to handle and keep track of SAS
     /// verification flows.
     verification_machine: VerificationMachine,
@@ -119,7 +122,7 @@ impl OlmMachine {
             device_id: device_id.into(),
             account: account.clone(),
             store: store.clone(),
-            outbound_group_sessions: HashMap::new(),
+            outbound_group_sessions: Arc::new(DashMap::new()),
             verification_machine: VerificationMachine::new(account, store),
         }
     }
@@ -165,7 +168,7 @@ impl OlmMachine {
             device_id,
             account,
             store,
-            outbound_group_sessions: HashMap::new(),
+            outbound_group_sessions: Arc::new(DashMap::new()),
             verification_machine,
         })
     }
@@ -802,7 +805,7 @@ impl OlmMachine {
     ///
     /// This also creates a matching inbound group session and saves that one in
     /// the store.
-    async fn create_outbound_group_session(&mut self, room_id: &RoomId) -> OlmResult<()> {
+    async fn create_outbound_group_session(&self, room_id: &RoomId) -> OlmResult<()> {
         let (outbound, inbound) = self.account.create_group_session_pair(room_id).await;
 
         let _ = self
@@ -818,6 +821,17 @@ impl OlmMachine {
         Ok(())
     }
 
+    /// Get an outbound group session for a room, if one exists.
+    ///
+    /// # Arguments
+    ///
+    /// * `room_id` - The id of the room for which we should get the outbound
+    /// group session.
+    fn get_outbound_group_session(&self, room_id: &RoomId) -> Option<OutboundGroupSession> {
+        #[allow(clippy::map_clone)]
+        self.outbound_group_sessions.get(room_id).map(|s| s.clone())
+    }
+
     /// Encrypt a room message for the given room.
     ///
     /// Beware that a group session needs to be shared before this method can be
@@ -844,9 +858,7 @@ impl OlmMachine {
         room_id: &RoomId,
         content: MessageEventContent,
     ) -> MegolmResult<EncryptedEventContent> {
-        let session = self.outbound_group_sessions.get(room_id);
-
-        let session = if let Some(s) = session {
+        let session = if let Some(s) = self.get_outbound_group_session(room_id) {
             s
         } else {
             panic!("Session wasn't created nor shared");
@@ -929,7 +941,7 @@ impl OlmMachine {
     ///
     /// Returns true if a session was invalidated, false if there was no session
     /// to invalidate.
-    pub fn invalidate_group_session(&mut self, room_id: &RoomId) -> bool {
+    pub fn invalidate_group_session(&self, room_id: &RoomId) -> bool {
         self.outbound_group_sessions.remove(room_id).is_some()
     }
 
@@ -943,7 +955,7 @@ impl OlmMachine {
     ///
     /// `users` - The list of users that should receive the group session.
     pub async fn share_group_session<'a, I>(
-        &mut self,
+        &self,
         room_id: &RoomId,
         users: I,
     ) -> OlmResult<Vec<OwnedToDeviceRequest>>
@@ -1538,7 +1550,7 @@ mod test {
 
     #[tokio::test]
     async fn tests_session_invalidation() {
-        let mut machine = OlmMachine::new(&user_id(), &alice_device_id());
+        let machine = OlmMachine::new(&user_id(), &alice_device_id());
         let room_id = room_id!("!test:example.org");
 
         machine
@@ -1754,7 +1766,7 @@ mod test {
 
     #[tokio::test]
     async fn test_room_key_sharing() {
-        let (mut alice, bob) = get_machine_pair_with_session().await;
+        let (alice, bob) = get_machine_pair_with_session().await;
 
         let room_id = room_id!("!test:example.org");
 
@@ -1800,7 +1812,7 @@ mod test {
 
     #[tokio::test]
     async fn test_megolm_encryption() {
-        let (mut alice, bob) = get_machine_pair_with_setup_sessions().await;
+        let (alice, bob) = get_machine_pair_with_setup_sessions().await;
         let room_id = room_id!("!test:example.org");
 
         let to_device_requests = alice