diff --git a/aider/coders/base_coder.py b/aider/coders/base_coder.py
index 033b40b63..701c0ecad 100755
--- a/aider/coders/base_coder.py
+++ b/aider/coders/base_coder.py
@@ -245,8 +245,6 @@ class Coder:
         self.verbose = verbose
         self.abs_fnames = set()
         self.abs_read_only_fnames = set()
-        if read_only_fnames:
-            self.abs_read_only_fnames = set(self.abs_root_path(fname) for fname in read_only_fnames)
 
         if cur_messages:
             self.cur_messages = cur_messages
@@ -321,6 +319,9 @@ class Coder:
         if not self.repo:
             self.find_common_root()
 
+        if read_only_fnames:
+            self.abs_read_only_fnames = set(self.abs_root_path(fname) for fname in read_only_fnames)
+
         if map_tokens is None:
             use_repo_map = main_model.use_repo_map
             map_tokens = 1024