diff --git a/src/grung/types.py b/src/grung/types.py
index 285787e..657f7b2 100644
--- a/src/grung/types.py
+++ b/src/grung/types.py
@@ -305,7 +305,7 @@ class FilePointer(Field):
         path = db.path / relpath
         path.parent.mkdir(parents=True, exist_ok=True)
         path.write_bytes(record[self.name])
-        record[self.name] = relpath
+        record[self.name] = str(relpath)
 
 
 @dataclass