diff --git a/mibios/umrad/fields.py b/mibios/umrad/fields.py
index 26950d2..eede8e7 100644
--- a/mibios/umrad/fields.py
+++ b/mibios/umrad/fields.py
@@ -193,6 +193,8 @@ def get_prep_value(self, value):
         elif self.root is None:
             return str(value)
         else:
+            if not isinstance(value, Path):
+                value = Path(value)
             return str(value.relative_to(self.root))
 
     def value_to_string(self, obj):