diff --git a/matrix_sdk_crypto/src/session_manager/group_sessions.rs b/matrix_sdk_crypto/src/session_manager/group_sessions.rs
index 6b3dde99..3c68e562 100644
--- a/matrix_sdk_crypto/src/session_manager/group_sessions.rs
+++ b/matrix_sdk_crypto/src/session_manager/group_sessions.rs
@@ -235,7 +235,12 @@ impl GroupSessionManager {
                 changed_sessions.push(session);
             }
 
-            messages.extend(message);
+            for (user, device_messages) in message.into_iter() {
+                messages
+                    .entry(user)
+                    .or_insert_with(BTreeMap::new)
+                    .extend(device_messages);
+            }
         }
 
         let id = Uuid::new_v4();
@@ -515,3 +520,86 @@ impl GroupSessionManager {
         Ok(requests)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use std::convert::TryFrom;
+
+    use matrix_sdk_common::{
+        api::r0::keys::{claim_keys, get_keys},
+        identifiers::{room_id, user_id, DeviceIdBox, UserId},
+        uuid::Uuid,
+    };
+    use matrix_sdk_test::response_from_file;
+    use serde_json::Value;
+
+    use crate::{EncryptionSettings, OlmMachine};
+
+    fn alice_id() -> UserId {
+        user_id!("@alice:example.org")
+    }
+
+    fn alice_device_id() -> DeviceIdBox {
+        "JLAFKJWSCS".into()
+    }
+
+    fn keys_query_response() -> get_keys::Response {
+        let data = include_bytes!("../../benches/keys_query.json");
+        let data: Value = serde_json::from_slice(data).unwrap();
+        let data = response_from_file(&data);
+        get_keys::Response::try_from(data).expect("Can't parse the keys upload response")
+    }
+
+    fn keys_claim_response() -> claim_keys::Response {
+        let data = include_bytes!("../../benches/keys_claim.json");
+        let data: Value = serde_json::from_slice(data).unwrap();
+        let data = response_from_file(&data);
+        claim_keys::Response::try_from(data).expect("Can't parse the keys upload response")
+    }
+
+    async fn machine() -> OlmMachine {
+        let keys_query = keys_query_response();
+        let keys_claim = keys_claim_response();
+        let uuid = Uuid::new_v4();
+
+        let machine = OlmMachine::new(&alice_id(), &alice_device_id());
+
+        machine
+            .mark_request_as_sent(&uuid, &keys_query)
+            .await
+            .unwrap();
+        machine
+            .mark_request_as_sent(&uuid, &keys_claim)
+            .await
+            .unwrap();
+
+        machine
+    }
+
+    #[tokio::test]
+    async fn test_sharing() {
+        let machine = machine().await;
+        let room_id = room_id!("!test:localhost");
+        let keys_claim = keys_claim_response();
+
+        let users: Vec<_> = keys_claim.one_time_keys.keys().collect();
+
+        let requests = machine
+            .share_group_session(
+                &room_id,
+                users.clone().into_iter(),
+                EncryptionSettings::default(),
+            )
+            .await
+            .unwrap();
+
+        let event_count = requests.iter().fold(0, |acc, r| {
+            acc + r.messages.values().fold(0, |acc, v| acc + v.len())
+        });
+
+        // The keys claim response has a couple of one-time keys with invalid
+        // signatures, thus only 148 sessions are actually created, we check
+        // that all 148 valid sessions get an room key.
+        assert_eq!(event_count, 148);
+    }
+}