diff --git a/aider/coders/editblock_coder.py b/aider/coders/editblock_coder.py
index 05803dd77..ffbcfc644 100644
--- a/aider/coders/editblock_coder.py
+++ b/aider/coders/editblock_coder.py
@@ -442,9 +442,8 @@ def find_original_update_blocks(content, fence=DEFAULT_FENCE, valid_fnames=None)
         # Check for SEARCH/REPLACE blocks
         if line.strip() == HEAD:
             try:
-                # if next line after HEAD is DIVIDER, it's a new file
-                next_line = lines[i + 1]
-                if next_line.strip() == DIVIDER:
+                # if next line after HEAD exists and is DIVIDER, it's a new file
+                if i + 1 < len(lines) and lines[i + 1].strip() == DIVIDER:
                     filename = find_filename(lines[max(0, i - 3) : i], fence, None)
                 else:
                     filename = find_filename(