diff --git a/aider/coders/base_coder.py b/aider/coders/base_coder.py
index 0987c9a84..2fbe55666 100755
--- a/aider/coders/base_coder.py
+++ b/aider/coders/base_coder.py
@@ -155,7 +155,7 @@ class Coder:
         if use_git:
             self.set_repo(fnames)
         else:
-            self.abs_fnames = [str(Path(fname).resolve()) for fname in fnames]
+            self.abs_fnames = set([str(Path(fname).resolve()) for fname in fnames])
 
         if self.repo:
             rel_repo_dir = os.path.relpath(self.repo.git_dir, os.getcwd())