diff --git a/flopy/mf6/mfpackage.py b/flopy/mf6/mfpackage.py
index 786b65d7c9..9b10e39428 100644
--- a/flopy/mf6/mfpackage.py
+++ b/flopy/mf6/mfpackage.py
@@ -1572,7 +1572,8 @@ def __init__(
                 )
             # only store the file name.  model relative path handled
             # internally
-            filename = os.path.split(filename)[-1]
+            if model_or_sim.type.lower() == "model":
+                filename = os.path.split(filename)[-1]
             self._filename = MFFileMgmt.string_to_file_path(filename)
         self.path, self.structure = model_or_sim.register_package(
             self, not loading_package, pname is None, filename is None