diff --git a/aider/coders/base_coder.py b/aider/coders/base_coder.py
index d788ad6a3..e837b7a34 100755
--- a/aider/coders/base_coder.py
+++ b/aider/coders/base_coder.py
@@ -364,7 +364,7 @@ class Coder:
         explain = f"""
 You *MUST* use {num_ticks} backticks, because some files contain {num_ticks-1} backticks already!"""
 
-        fence = "`" * num_ticks
+        self.fence_ticks = "`" * num_ticks
 
         number_mapping = {
             3: "triple",
@@ -375,7 +375,7 @@ You *MUST* use {num_ticks} backticks, because some files contain {num_ticks-1} b
 
         prompt = prompt.format(
             num_ticks=num_ticks_name,
-            fence=fence,
+            fence=self.fence_ticks,
             num_ticks_explanation=explain,
         )
 
diff --git a/aider/coders/wholefile_coder.py b/aider/coders/wholefile_coder.py
index 48e3339e3..a7cd11e01 100644
--- a/aider/coders/wholefile_coder.py
+++ b/aider/coders/wholefile_coder.py
@@ -36,7 +36,7 @@ class WholeFileCoder(Coder):
         fname = None
         new_lines = []
         for i, line in enumerate(lines):
-            if line.startswith("```"):
+            if line.startswith(self.fence_ticks):
                 if fname is not None:
                     # ending an existing block
                     saw_fname = None
@@ -77,7 +77,9 @@ class WholeFileCoder(Coder):
                         fname = chat_files[0]
                     else:
                         # TODO: sense which file it is by diff size
-                        raise ValueError("No filename provided before ``` in file listing")
+                        raise ValueError(
+                            f"No filename provided before {self.fence_ticks} in file listing"
+                        )
 
             elif fname is not None:
                 new_lines.append(line)