diff --git a/src/api/server_server.rs b/src/api/server_server.rs
index 74f7a1b0..8a8a77d8 100644
--- a/src/api/server_server.rs
+++ b/src/api/server_server.rs
@@ -1860,7 +1860,7 @@ pub(crate) async fn create_invite_route(
                         events: vec![pdu.to_room_event()],
                         txn_id:
                             base64::engine::general_purpose::URL_SAFE_NO_PAD
-                                .encode(utils::calculate_hash(&[pdu
+                                .encode(utils::calculate_hash([pdu
                                     .event_id()
                                     .as_bytes()]))
                                 .into(),
diff --git a/src/service/rooms/state.rs b/src/service/rooms/state.rs
index 7c6a25e4..485d2b8c 100644
--- a/src/service/rooms/state.rs
+++ b/src/service/rooms/state.rs
@@ -133,9 +133,8 @@ impl Service {
         let previous_shortstatehash =
             self.db.get_room_shortstatehash(room_id)?;
 
-        let state_hash = calculate_hash(
-            &state_ids_compressed.iter().map(|s| &s[..]).collect::<Vec<_>>(),
-        );
+        let state_hash =
+            calculate_hash(state_ids_compressed.iter().map(|s| &s[..]));
 
         let (shortstatehash, already_existed) =
             services().rooms.short.get_or_create_shortstatehash(&state_hash)?;
diff --git a/src/service/rooms/state_compressor.rs b/src/service/rooms/state_compressor.rs
index f6a7d407..a545cf5e 100644
--- a/src/service/rooms/state_compressor.rs
+++ b/src/service/rooms/state_compressor.rs
@@ -283,10 +283,7 @@ impl Service {
             services().rooms.state.get_room_shortstatehash(room_id)?;
 
         let state_hash = utils::calculate_hash(
-            &new_state_ids_compressed
-                .iter()
-                .map(|bytes| &bytes[..])
-                .collect::<Vec<_>>(),
+            new_state_ids_compressed.iter().map(|bytes| &bytes[..]),
         );
 
         let (new_shortstatehash, already_existed) =
diff --git a/src/service/sending.rs b/src/service/sending.rs
index bc4c33d6..c486701e 100644
--- a/src/service/sending.rs
+++ b/src/service/sending.rs
@@ -755,17 +755,10 @@ async fn handle_appservice_event(
         appservice::event::push_events::v1::Request {
             events: pdu_jsons,
             txn_id: general_purpose::URL_SAFE_NO_PAD
-                .encode(calculate_hash(
-                    &events
-                        .iter()
-                        .map(|e| match e {
-                            SendingEventType::Edu(b) => {
-                                b.json().get().as_bytes()
-                            }
-                            SendingEventType::Pdu(b) => b.as_bytes(),
-                        })
-                        .collect::<Vec<_>>(),
-                ))
+                .encode(calculate_hash(events.iter().map(|e| match e {
+                    SendingEventType::Edu(b) => b.json().get().as_bytes(),
+                    SendingEventType::Pdu(b) => b.as_bytes(),
+                })))
                 .into(),
         },
     )
@@ -902,17 +895,10 @@ async fn handle_federation_event(
             edus: edu_jsons,
             origin_server_ts: MilliSecondsSinceUnixEpoch::now(),
             transaction_id: general_purpose::URL_SAFE_NO_PAD
-                .encode(calculate_hash(
-                    &events
-                        .iter()
-                        .map(|e| match e {
-                            SendingEventType::Edu(b) => {
-                                b.json().get().as_bytes()
-                            }
-                            SendingEventType::Pdu(b) => b.as_bytes(),
-                        })
-                        .collect::<Vec<_>>(),
-                ))
+                .encode(calculate_hash(events.iter().map(|e| match e {
+                    SendingEventType::Edu(b) => b.json().get().as_bytes(),
+                    SendingEventType::Pdu(b) => b.as_bytes(),
+                })))
                 .into(),
         },
         false,
diff --git a/src/utils.rs b/src/utils.rs
index 42c15f88..30be1bad 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -106,9 +106,18 @@ where
 }
 
 #[tracing::instrument(skip(keys))]
-pub(crate) fn calculate_hash(keys: &[&[u8]]) -> Vec<u8> {
-    // We only hash the pdu's event ids, not the whole pdu
-    let bytes = keys.join(&0xFF);
+pub(crate) fn calculate_hash<'a, I, T>(keys: I) -> Vec<u8>
+where
+    I: IntoIterator<Item = T>,
+    T: AsRef<[u8]>,
+{
+    let mut bytes = Vec::new();
+    for (i, key) in keys.into_iter().enumerate() {
+        if i != 0 {
+            bytes.push(0xFF);
+        }
+        bytes.extend_from_slice(key.as_ref());
+    }
     let hash = digest::digest(&digest::SHA256, &bytes);
     hash.as_ref().to_owned()
 }