diff --git a/src/borg/locking.py b/src/borg/locking.py
index c21518d93..0fc092750 100644
--- a/src/borg/locking.py
+++ b/src/borg/locking.py
@@ -204,13 +204,13 @@ def break_lock(self):
 
     def migrate_lock(self, old_id, new_id):
         """migrate the lock ownership from old_id to new_id"""
-        if self.id == old_id:
-            new_unique_name = os.path.join(self.path, "%s.%d-%x" % new_id)
-            if self.is_locked() and self.by_me():
-                with open(new_unique_name, "wb"):
-                    pass
-                os.unlink(self.unique_name)
-            self.id, self.unique_name = new_id, new_unique_name
+        assert self.id == old_id
+        new_unique_name = os.path.join(self.path, "%s.%d-%x" % new_id)
+        if self.is_locked() and self.by_me():
+            with open(new_unique_name, "wb"):
+                pass
+            os.unlink(self.unique_name)
+        self.id, self.unique_name = new_id, new_unique_name
 
 
 class LockRoster:
@@ -283,22 +283,22 @@ def modify(self, key, op):
 
     def migrate_lock(self, key, old_id, new_id):
         """migrate the lock ownership from old_id to new_id"""
-        if self.id == old_id:
-            # need to temporarily switch off stale lock killing as we want to
-            # rather migrate than kill them (at least the one made by old_id).
-            killing, self.kill_stale_locks = self.kill_stale_locks, False
+        assert self.id == old_id
+        # need to temporarily switch off stale lock killing as we want to
+        # rather migrate than kill them (at least the one made by old_id).
+        killing, self.kill_stale_locks = self.kill_stale_locks, False
+        try:
             try:
-                try:
-                    self.modify(key, REMOVE)
-                except KeyError:
-                    # entry was not there, so no need to add a new one, but still update our id
-                    self.id = new_id
-                else:
-                    # old entry removed, update our id and add a updated entry
-                    self.id = new_id
-                    self.modify(key, ADD)
-            finally:
-                self.kill_stale_locks = killing
+                self.modify(key, REMOVE)
+            except KeyError:
+                # entry was not there, so no need to add a new one, but still update our id
+                self.id = new_id
+            else:
+                # old entry removed, update our id and add a updated entry
+                self.id = new_id
+                self.modify(key, ADD)
+        finally:
+            self.kill_stale_locks = killing
 
 
 class Lock:
@@ -404,12 +404,12 @@ def break_lock(self):
         self._lock.break_lock()
 
     def migrate_lock(self, old_id, new_id):
-        if self.id == old_id:
-            self.id = new_id
-            if self.is_exclusive:
+        assert self.id == old_id
+        self.id = new_id
+        if self.is_exclusive:
+            self._lock.migrate_lock(old_id, new_id)
+            self._roster.migrate_lock(EXCLUSIVE, old_id, new_id)
+        else:
+            with self._lock:
                 self._lock.migrate_lock(old_id, new_id)
-                self._roster.migrate_lock(EXCLUSIVE, old_id, new_id)
-            else:
-                with self._lock:
-                    self._lock.migrate_lock(old_id, new_id)
-                    self._roster.migrate_lock(SHARED, old_id, new_id)
+                self._roster.migrate_lock(SHARED, old_id, new_id)