diff --git a/xugrid/ugrid/ugridbase.py b/xugrid/ugrid/ugridbase.py
index c72e0700..77c940f8 100644
--- a/xugrid/ugrid/ugridbase.py
+++ b/xugrid/ugrid/ugridbase.py
@@ -485,7 +485,8 @@ def _prepare_connectivity(
 
     def _set_fillvalue(self, connectivity: IntArray) -> IntArray:
         c = connectivity.copy()
-        c[c == FILL_VALUE] = self.fill_value
+        if self.fill_value != FILL_VALUE:
+            c[c == FILL_VALUE] = self.fill_value
         return c
 
     def _precheck(self, multi_index):