From 2d31350d5d04b038a1a2d3e6040783a336665e74 Mon Sep 17 00:00:00 2001
From: A Sivasubramanian Manoj <sivasubramanianmanoj2310533@ssn.edu.in>
Date: Thu, 9 Jul 2026 11:01:59 +0000
Subject: [PATCH] Fix invalid group reference in
 revert_checkpoint_conversion_mapping (#2028)

Signed-off-by: A Sivasubramanian Manoj <sivasubramanianmanoj2310533@ssn.edu.in>
---
 auto_round/utils/common.py        | 5 ++++-
 test/test_cpu/utils/test_utils.py | 8 ++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/auto_round/utils/common.py b/auto_round/utils/common.py
index 236d56c05..4af0291a2 100644
--- a/auto_round/utils/common.py
+++ b/auto_round/utils/common.py
@@ -1191,7 +1191,10 @@ def revert_checkpoint_conversion_mapping(name: str, key_mapping: dict[str, str])
             target_patterns = [target_patterns]
         for target_pattern in target_patterns:
             source_pattern = source_pattern.lstrip("^")  # strip off un-needed chars and patterns
-            source_pattern = re.sub(r"\(.*\)", "", source_pattern)
+            # Skip stripping the capture group if the target backreferences it,
+            # otherwise re.subn raises "invalid group reference".
+            if not re.search(r"\\g?<?\d+>?", target_pattern):
+                source_pattern = re.sub(r"\(.*\)", "", source_pattern)
 
             # Weight-conversion reverse mappings may expose bare tensor names
             # such as "weight" -> ".weight_packed". Treat those as terminal
diff --git a/test/test_cpu/utils/test_utils.py b/test/test_cpu/utils/test_utils.py
index 587fe57d7..463f8cbb4 100644
--- a/test/test_cpu/utils/test_utils.py
+++ b/test/test_cpu/utils/test_utils.py
@@ -56,6 +56,14 @@ def test_revert_checkpoint_conversion_mapping_does_not_rewrite_quantized_tensor_
     )
 
 
+def test_revert_checkpoint_conversion_mapping_handles_backreference_patterns():
+    mapping = {r"^model\.language_model\.(.+)$": r"model.\1"}
+
+    converted = revert_checkpoint_conversion_mapping("model.language_model.layers.0.self_attn.q_proj.weight", mapping)
+
+    assert converted == "model.layers.0.self_attn.q_proj.weight"
+
+
 def test_preserve_original_visual_block_name():
     # Single visual block name
     assert preserve_original_visual_block_name("model.visual.blocks", "visual.blocks") == "model.visual.blocks"