diff --git a/aider/io.py b/aider/io.py
index f975c7352..57d4421c5 100644
--- a/aider/io.py
+++ b/aider/io.py
@@ -360,7 +360,7 @@ class InputOutput:
         show = ""
         if rel_fnames:
             rel_read_only_fnames = [
-                os.path.relpath(fname, root) for fname in (abs_read_only_fnames or [])
+                get_rel_fname(fname, root) for fname in (abs_read_only_fnames or [])
             ]
             show = self.format_files_for_input(rel_fnames, rel_read_only_fnames)
         if edit_format:
@@ -712,3 +712,10 @@ class InputOutput:
             editable_files.append(f"{full_path}")
 
         return "\n".join(read_only_files + editable_files) + "\n"
+
+
+def get_rel_fname(self, fname, root):
+    try:
+        return os.path.relpath(fname, root)
+    except ValueError:
+        return fname