diff --git a/aider/utils.py b/aider/utils.py
index 3da9f3584..c1053bec1 100644
--- a/aider/utils.py
+++ b/aider/utils.py
@@ -67,7 +67,7 @@ def replace_part_with_missing_leading_whitespace(whole, part, replace):
     # If all lines in the part start with whitespace, then honor it.
     # But GPT often outdents the part and replace blocks completely,
     # thereby discarding the actual leading whitespace in the file.
-    if all(pline[0].isspace() for pline in part_lines):
+    if all((len(pline) > 0 and pline[0].isspace()) for pline in part_lines):
         return
 
     for i in range(len(whole_lines) - len(part_lines) + 1):