diff --git a/scmrepo/git/backend/dulwich/__init__.py b/scmrepo/git/backend/dulwich/__init__.py
index 761b5548..cbffba18 100644
--- a/scmrepo/git/backend/dulwich/__init__.py
+++ b/scmrepo/git/backend/dulwich/__init__.py
@@ -78,8 +78,8 @@ def scandir(self) -> Iterable["DulwichObject"]:
                 self.repo, entry.path.decode(), entry.mode, entry.sha
             )
 
-    @property
-    def size(self) -> int:
+    @cached_property
+    def size(self) -> int:  # pylint: disable=invalid-overridden-method
         return len(self.repo[self.sha].as_raw_string())
 
     @property
diff --git a/scmrepo/git/backend/pygit2.py b/scmrepo/git/backend/pygit2.py
index 20f82a42..aff2d2c4 100644
--- a/scmrepo/git/backend/pygit2.py
+++ b/scmrepo/git/backend/pygit2.py
@@ -62,8 +62,8 @@ def mode(self):
             return stat.S_IFDIR
         return self.obj.filemode
 
-    @property
-    def size(self) -> int:
+    @cached_property
+    def size(self) -> int:  # pylint: disable=invalid-overridden-method
         try:
             return len(self.obj.read_raw())
         except KeyError: