diff --git a/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data.rs b/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data.rs
index 309a11c3152..d1d69262cbc 100644
--- a/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data.rs
+++ b/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data.rs
@@ -72,7 +72,7 @@ pub enum SenderData {
         device_id: Option<OwnedDeviceId>,
 
         /// The cross-signing key of the user who established this session.
-        master_key: Ed25519PublicKey,
+        master_key: Box<Ed25519PublicKey>,
 
         /// Whether, at the time we checked the signature on the device,
         /// we had actively verified that `master_key` belongs to the user.
diff --git a/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data_finder.rs b/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data_finder.rs
index 581aaa77013..52f104b3218 100644
--- a/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data_finder.rs
+++ b/crates/matrix-sdk-crypto/src/olm/group_sessions/sender_data_finder.rs
@@ -266,6 +266,7 @@ impl<'a> SenderDataFinder<'a> {
 
         if let Some(master_key) = master_key {
             // We have user_id and master_key for the user sending the to-device message.
+            let master_key = Box::new(master_key);
             let master_key_verified = sender_device.is_cross_signing_trusted();
             SenderData::SenderKnown { user_id, device_id, master_key, master_key_verified }
         } else {
@@ -448,7 +449,7 @@ mod tests {
         );
         assert_eq!(user_id, setup.sender.user_id);
         assert_eq!(device_id.unwrap(), setup.sender_device.device_id());
-        assert_eq!(master_key, setup.sender_master_key());
+        assert_eq!(*master_key, setup.sender_master_key());
         assert!(!master_key_verified);
     }
 
@@ -477,7 +478,7 @@ mod tests {
         );
         assert_eq!(user_id, setup.sender.user_id);
         assert_eq!(device_id.unwrap(), setup.sender_device.device_id());
-        assert_eq!(master_key, setup.sender_master_key());
+        assert_eq!(*master_key, setup.sender_master_key());
         assert!(!master_key_verified);
     }
 
@@ -507,7 +508,7 @@ mod tests {
         );
         assert_eq!(user_id, setup.sender.user_id);
         assert_eq!(device_id.unwrap(), setup.sender_device.device_id());
-        assert_eq!(master_key, setup.sender_master_key());
+        assert_eq!(*master_key, setup.sender_master_key());
         assert!(!master_key_verified);
     }
 
@@ -536,7 +537,7 @@ mod tests {
         );
         assert_eq!(user_id, setup.sender.user_id);
         assert_eq!(device_id.unwrap(), setup.sender_device.device_id());
-        assert_eq!(master_key, setup.sender_master_key());
+        assert_eq!(*master_key, setup.sender_master_key());
         assert!(!master_key_verified);
     }
 
@@ -604,7 +605,7 @@ mod tests {
         );
         assert_eq!(user_id, setup.sender.user_id);
         assert_eq!(device_id.unwrap(), setup.sender_device.device_id());
-        assert_eq!(master_key, setup.sender_master_key());
+        assert_eq!(*master_key, setup.sender_master_key());
         // Including the fact that it was verified
         assert!(master_key_verified);
     }
@@ -637,7 +638,7 @@ mod tests {
         );
         assert_eq!(user_id, setup.sender.user_id);
         assert_eq!(device_id.unwrap(), setup.sender_device.device_id());
-        assert_eq!(master_key, setup.sender_master_key());
+        assert_eq!(*master_key, setup.sender_master_key());
         // Including the fact that it was verified
         assert!(master_key_verified);
     }
@@ -661,7 +662,7 @@ mod tests {
         );
         assert_eq!(user_id, setup.sender.user_id);
         assert_eq!(device_id.unwrap(), setup.sender_device.device_id());
-        assert_eq!(master_key, setup.sender_master_key());
+        assert_eq!(*master_key, setup.sender_master_key());
         assert!(!master_key_verified);
     }