diff --git a/crates/handlers/src/compat/login.rs b/crates/handlers/src/compat/login.rs
index c5e9cd432..d75b4f8bd 100644
--- a/crates/handlers/src/compat/login.rs
+++ b/crates/handlers/src/compat/login.rs
@@ -411,7 +411,7 @@ pub(crate) async fn post(
     // Now we can create the device on the homeserver, without holding the
     // transaction
     if let Err(err) = homeserver
-        .create_device(
+        .upsert_device(
             &user.username,
             device.as_str(),
             session.human_name.as_deref(),
diff --git a/crates/handlers/src/graphql/mutations/oauth2_session.rs b/crates/handlers/src/graphql/mutations/oauth2_session.rs
index 27f253394..55723efc5 100644
--- a/crates/handlers/src/graphql/mutations/oauth2_session.rs
+++ b/crates/handlers/src/graphql/mutations/oauth2_session.rs
@@ -215,7 +215,7 @@ impl OAuth2SessionMutations {
         for scope in &*session.scope {
             if let Some(device) = Device::from_scope_token(scope) {
                 homeserver
-                    .create_device(&user.username, device.as_str(), None)
+                    .upsert_device(&user.username, device.as_str(), None)
                     .await
                     .context("Failed to provision device")?;
             }
diff --git a/crates/handlers/src/oauth2/token.rs b/crates/handlers/src/oauth2/token.rs
index a56cf763f..768f79d35 100644
--- a/crates/handlers/src/oauth2/token.rs
+++ b/crates/handlers/src/oauth2/token.rs
@@ -578,7 +578,7 @@ async fn authorization_code_grant(
     for scope in &*session.scope {
         if let Some(device) = Device::from_scope_token(scope) {
             homeserver
-                .create_device(
+                .upsert_device(
                     &browser_session.user.username,
                     device.as_str(),
                     Some(&device_name),
@@ -957,7 +957,7 @@ async fn device_code_grant(
     for scope in &*session.scope {
         if let Some(device) = Device::from_scope_token(scope) {
             homeserver
-                .create_device(&browser_session.user.username, device.as_str(), None)
+                .upsert_device(&browser_session.user.username, device.as_str(), None)
                 .await
                 .map_err(RouteError::ProvisionDeviceFailed)?;
         }
diff --git a/crates/matrix-synapse/src/legacy.rs b/crates/matrix-synapse/src/legacy.rs
index 43764d17e..d07e6b5d5 100644
--- a/crates/matrix-synapse/src/legacy.rs
+++ b/crates/matrix-synapse/src/legacy.rs
@@ -308,7 +308,7 @@ impl HomeserverConnection for SynapseConnection {
     }
 
     #[tracing::instrument(
-        name = "homeserver.create_device",
+        name = "homeserver.upsert_device",
         skip_all,
         fields(
             matrix.homeserver = self.homeserver,
@@ -317,7 +317,7 @@ impl HomeserverConnection for SynapseConnection {
         ),
         err(Debug),
     )]
-    async fn create_device(
+    async fn upsert_device(
         &self,
         localpart: &str,
         device_id: &str,
@@ -513,7 +513,7 @@ impl HomeserverConnection for SynapseConnection {
         // Then, create the devices that are missing. There is no batching API to do
         // this, so we do this sequentially, which is fine as the API is idempotent.
         for device_id in devices.difference(&existing_devices) {
-            self.create_device(localpart, device_id, None).await?;
+            self.upsert_device(localpart, device_id, None).await?;
         }
 
         Ok(())
diff --git a/crates/matrix-synapse/src/modern.rs b/crates/matrix-synapse/src/modern.rs
index 4f7172eca..454afbf9f 100644
--- a/crates/matrix-synapse/src/modern.rs
+++ b/crates/matrix-synapse/src/modern.rs
@@ -227,7 +227,7 @@ impl HomeserverConnection for SynapseConnection {
     }
 
     #[tracing::instrument(
-        name = "homeserver.create_device",
+        name = "homeserver.upsert_device",
         skip_all,
         fields(
             matrix.homeserver = self.homeserver,
@@ -236,7 +236,7 @@ impl HomeserverConnection for SynapseConnection {
         ),
         err(Debug),
     )]
-    async fn create_device(
+    async fn upsert_device(
         &self,
         localpart: &str,
         device_id: &str,
@@ -257,7 +257,7 @@ impl HomeserverConnection for SynapseConnection {
         };
 
         let response = self
-            .post("_synapse/mas/create_device")
+            .post("_synapse/mas/upsert_device")
             .json(&body)
             .send_traced()
             .await
diff --git a/crates/matrix/src/lib.rs b/crates/matrix/src/lib.rs
index 012fba216..34c502f81 100644
--- a/crates/matrix/src/lib.rs
+++ b/crates/matrix/src/lib.rs
@@ -254,7 +254,7 @@ pub trait HomeserverConnection: Send + Sync {
     ///
     /// Returns an error if the homeserver is unreachable or the device could
     /// not be created.
-    async fn create_device(
+    async fn upsert_device(
         &self,
         localpart: &str,
         device_id: &str,
@@ -396,14 +396,14 @@ impl<T: HomeserverConnection + Send + Sync + ?Sized> HomeserverConnection for &T
         (**self).is_localpart_available(localpart).await
     }
 
-    async fn create_device(
+    async fn upsert_device(
         &self,
         localpart: &str,
         device_id: &str,
         initial_display_name: Option<&str>,
     ) -> Result<(), anyhow::Error> {
         (**self)
-            .create_device(localpart, device_id, initial_display_name)
+            .upsert_device(localpart, device_id, initial_display_name)
             .await
     }
 
@@ -474,14 +474,14 @@ impl<T: HomeserverConnection + ?Sized> HomeserverConnection for Arc<T> {
         (**self).is_localpart_available(localpart).await
     }
 
-    async fn create_device(
+    async fn upsert_device(
         &self,
         localpart: &str,
         device_id: &str,
         initial_display_name: Option<&str>,
     ) -> Result<(), anyhow::Error> {
         (**self)
-            .create_device(localpart, device_id, initial_display_name)
+            .upsert_device(localpart, device_id, initial_display_name)
             .await
     }
 
diff --git a/crates/matrix/src/mock.rs b/crates/matrix/src/mock.rs
index ce2c61000..0c315ff97 100644
--- a/crates/matrix/src/mock.rs
+++ b/crates/matrix/src/mock.rs
@@ -109,7 +109,7 @@ impl crate::HomeserverConnection for HomeserverConnection {
         Ok(!users.contains_key(&mxid))
     }
 
-    async fn create_device(
+    async fn upsert_device(
         &self,
         localpart: &str,
         device_id: &str,
@@ -223,7 +223,7 @@ mod tests {
         assert_eq!(conn.mxid("test"), mxid);
 
         assert!(conn.query_user("test").await.is_err());
-        assert!(conn.create_device("test", device, None).await.is_err());
+        assert!(conn.upsert_device("test", device, None).await.is_err());
         assert!(conn.delete_device("test", device).await.is_err());
 
         let request = ProvisionRequest::new("test", "test")
@@ -254,9 +254,9 @@ mod tests {
         assert!(conn.delete_device("test", device).await.is_ok());
 
         // Create the device
-        assert!(conn.create_device("test", device, None).await.is_ok());
+        assert!(conn.upsert_device("test", device, None).await.is_ok());
         // Create the same device again
-        assert!(conn.create_device("test", device, None).await.is_ok());
+        assert!(conn.upsert_device("test", device, None).await.is_ok());
 
         // XXX: there is no API to query devices yet in the trait
         // Delete the device
diff --git a/crates/matrix/src/readonly.rs b/crates/matrix/src/readonly.rs
index 39f36204f..2efa935f9 100644
--- a/crates/matrix/src/readonly.rs
+++ b/crates/matrix/src/readonly.rs
@@ -40,7 +40,7 @@ impl<C: HomeserverConnection> HomeserverConnection for ReadOnlyHomeserverConnect
         self.inner.is_localpart_available(localpart).await
     }
 
-    async fn create_device(
+    async fn upsert_device(
         &self,
         _localpart: &str,
         _device_id: &str,