diff --git a/tests/test_peft_weight_converter_compat.py b/tests/test_peft_weight_converter_compat.py
new file mode 100644
index 0000000000..62f17f0f45
--- /dev/null
+++ b/tests/test_peft_weight_converter_compat.py
@@ -0,0 +1,259 @@
+import importlib.util
+import inspect
+import sys
+import threading
+import types
+from pathlib import Path
+
+import pytest
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+IMPORT_FIXES = REPO_ROOT / "unsloth" / "import_fixes.py"
+
+
+def _load_patch_function():
+    spec = importlib.util.spec_from_file_location(
+        "_unsloth_import_fixes_under_test", IMPORT_FIXES
+    )
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module.patch_peft_weight_converter_compatibility
+
+
+def _install_fake_peft(twc_namespace):
+    peft_pkg = types.ModuleType("peft")
+    peft_pkg.__path__ = []
+    peft_utils = types.ModuleType("peft.utils")
+    peft_utils.__path__ = []
+    twc = types.ModuleType("peft.utils.transformers_weight_conversion")
+    for k, v in twc_namespace.items():
+        setattr(twc, k, v)
+    peft_utils.transformers_weight_conversion = twc
+    sys.modules["peft"] = peft_pkg
+    sys.modules["peft.utils"] = peft_utils
+    sys.modules["peft.utils.transformers_weight_conversion"] = twc
+    return twc
+
+
+@pytest.fixture(autouse = True)
+def _restore_peft_modules():
+    saved = {
+        k: sys.modules.get(k)
+        for k in (
+            "peft",
+            "peft.utils",
+            "peft.utils.transformers_weight_conversion",
+        )
+    }
+    yield
+    for k, v in saved.items():
+        if v is None:
+            sys.modules.pop(k, None)
+        else:
+            sys.modules[k] = v
+
+
+class _LegacyConverter:
+    def __init__(self, source_patterns, target_patterns, operations):
+        self.source_patterns = source_patterns
+        self.target_patterns = target_patterns
+        self.operations = operations
+        self.distributed_operation = None
+        self.quantization_operation = None
+
+
+class _ModernConverter:
+    def __init__(
+        self,
+        source_patterns,
+        target_patterns,
+        operations,
+        distributed_operation = None,
+        quantization_operation = None,
+    ):
+        self.source_patterns = source_patterns
+        self.target_patterns = target_patterns
+        self.operations = operations
+        self.distributed_operation = distributed_operation
+        self.quantization_operation = quantization_operation
+
+
+def _make_legacy_converter():
+    return _LegacyConverter(["src.*"], ["tgt.*"], [])
+
+
+def _make_modern_converter():
+    return _ModernConverter(["src.*"], ["tgt.*"], [])
+
+
+def _build_that_calls_init(weight_conversions, adapter_name, peft_config = None):
+    out = []
+    for c in weight_conversions or []:
+        out.append(
+            c.__class__(
+                source_patterns = c.source_patterns,
+                target_patterns = c.target_patterns,
+                operations = c.operations,
+                distributed_operation = "dist-x",
+                quantization_operation = "quant-y",
+            )
+        )
+    return out
+
+
+def test_two_arg_call_preserves_upstream_signature():
+    twc = _install_fake_peft({"build_peft_weight_mapping": _build_that_calls_init})
+    patch = _load_patch_function()
+    patch()
+
+    sig = inspect.signature(twc.build_peft_weight_mapping)
+    assert "peft_config" in sig.parameters
+    assert sig.parameters["peft_config"].default is None
+
+    out = twc.build_peft_weight_mapping([_make_legacy_converter()], "default")
+    assert len(out) == 1
+    assert out[0].distributed_operation == "dist-x"
+    assert out[0].quantization_operation == "quant-y"
+
+
+def test_legacy_init_succeeds_after_patch():
+    twc = _install_fake_peft({"build_peft_weight_mapping": _build_that_calls_init})
+    patch = _load_patch_function()
+    patch()
+
+    out = twc.build_peft_weight_mapping([_make_legacy_converter()], "default", None)
+    assert len(out) == 1
+    assert out[0].distributed_operation == "dist-x"
+    assert out[0].quantization_operation == "quant-y"
+
+
+def test_modern_init_not_patched():
+    twc = _install_fake_peft({"build_peft_weight_mapping": _build_that_calls_init})
+    pre_init = _ModernConverter.__init__
+    patch = _load_patch_function()
+    patch()
+
+    twc.build_peft_weight_mapping([_make_modern_converter()], "default", None)
+    assert _ModernConverter.__init__ is pre_init
+
+
+def test_class_init_restored_after_call():
+    twc = _install_fake_peft({"build_peft_weight_mapping": _build_that_calls_init})
+    pre_init = _LegacyConverter.__init__
+    patch = _load_patch_function()
+    patch()
+
+    twc.build_peft_weight_mapping([_make_legacy_converter()], "default", None)
+    assert _LegacyConverter.__init__ is pre_init
+
+
+def test_class_init_restored_after_original_build_raises():
+    def _raise(weight_conversions, adapter_name, peft_config = None):
+        raise RuntimeError("simulated PEFT failure")
+
+    twc = _install_fake_peft({"build_peft_weight_mapping": _raise})
+    pre_init = _LegacyConverter.__init__
+    patch = _load_patch_function()
+    patch()
+
+    with pytest.raises(RuntimeError):
+        twc.build_peft_weight_mapping([_make_legacy_converter()], "default", None)
+    assert _LegacyConverter.__init__ is pre_init
+
+
+def test_partial_patch_restored_when_inspect_signature_raises_mid_loop():
+    twc = _install_fake_peft({"build_peft_weight_mapping": _build_that_calls_init})
+    pre_legacy = _LegacyConverter.__init__
+
+    class _BadInitConverter:
+        def __init__(self, source_patterns, target_patterns, operations):
+            self.source_patterns = source_patterns
+            self.target_patterns = target_patterns
+            self.operations = operations
+
+    pre_bad = _BadInitConverter.__init__
+    patch = _load_patch_function()
+    patch()
+
+    real_signature = inspect.signature
+
+    def _fake_signature(callable_):
+        if callable_ is _BadInitConverter.__init__:
+            raise ValueError("inspect.signature failed mid-loop")
+        return real_signature(callable_)
+
+    inspect.signature = _fake_signature
+    try:
+        legacy = _LegacyConverter(["src.*"], ["tgt.*"], [])
+        bad = _BadInitConverter.__new__(_BadInitConverter)
+        bad.source_patterns = ["src.*"]
+        bad.target_patterns = ["tgt.*"]
+        bad.operations = []
+        with pytest.raises(ValueError):
+            twc.build_peft_weight_mapping([legacy, bad], "default", None)
+    finally:
+        inspect.signature = real_signature
+
+    assert _LegacyConverter.__init__ is pre_legacy
+    assert _BadInitConverter.__init__ is pre_bad
+
+
+def test_idempotent_install_does_not_double_wrap():
+    twc = _install_fake_peft({"build_peft_weight_mapping": _build_that_calls_init})
+    patch = _load_patch_function()
+    patch()
+    first_wrapped = twc.build_peft_weight_mapping
+    patch()
+    assert twc.build_peft_weight_mapping is first_wrapped
+
+
+def test_concurrent_legacy_calls_no_typeerror():
+    import time
+
+    def _slow_build(weight_conversions, adapter_name, peft_config = None):
+        time.sleep(0.05)
+        return _build_that_calls_init(weight_conversions, adapter_name, peft_config)
+
+    twc = _install_fake_peft({"build_peft_weight_mapping": _slow_build})
+    patch = _load_patch_function()
+    patch()
+
+    errors = []
+    results = []
+    start = threading.Event()
+
+    def _worker():
+        start.wait(timeout = 10)
+        try:
+            out = twc.build_peft_weight_mapping(
+                [_make_legacy_converter()], "default", None
+            )
+            results.append(out)
+        except Exception as e:
+            errors.append(e)
+
+    threads = [threading.Thread(target = _worker) for _ in range(8)]
+    for t in threads:
+        t.start()
+    start.set()
+    for t in threads:
+        t.join(timeout = 15)
+
+    assert errors == []
+    assert len(results) == 8
+    for out in results:
+        assert out[0].distributed_operation == "dist-x"
+        assert out[0].quantization_operation == "quant-y"
+    assert _LegacyConverter.__init__.__qualname__.startswith("_LegacyConverter")
+
+
+def test_empty_conversions_short_circuits_without_patching():
+    twc = _install_fake_peft({"build_peft_weight_mapping": _build_that_calls_init})
+    pre_init = _LegacyConverter.__init__
+    patch = _load_patch_function()
+    patch()
+
+    out = twc.build_peft_weight_mapping([], "default", None)
+    assert out == []
+    assert _LegacyConverter.__init__ is pre_init
diff --git a/unsloth/__init__.py b/unsloth/__init__.py
index 52114bb544..9db9ae0a32 100644
--- a/unsloth/__init__.py
+++ b/unsloth/__init__.py
@@ -153,6 +153,7 @@
     patch_torchcodec_audio_decoder,
     disable_torchcodec_if_broken,
     disable_broken_wandb,
+    patch_peft_weight_converter_compatibility,
 )
 
 fix_xformers_performance_issue()
@@ -176,6 +177,7 @@
 patch_torchcodec_audio_decoder()
 disable_torchcodec_if_broken()
 disable_broken_wandb()
+patch_peft_weight_converter_compatibility()
 
 del fix_xformers_performance_issue
 del fix_vllm_aimv2_issue
@@ -197,6 +199,7 @@
 del patch_torchcodec_audio_decoder
 del disable_torchcodec_if_broken
 del disable_broken_wandb
+del patch_peft_weight_converter_compatibility
 
 # Torch 2.4 has including_emulation
 if DEVICE_TYPE == "cuda":
diff --git a/unsloth/import_fixes.py b/unsloth/import_fixes.py
index 6cebad7939..f1fba0ce91 100644
--- a/unsloth/import_fixes.py
+++ b/unsloth/import_fixes.py
@@ -25,6 +25,7 @@
 import warnings
 import sys
 import functools
+import inspect
 
 # We cannot do from unsloth_zoo.log import logger since FBGEMM might cause seg faults.
 UNSLOTH_ENABLE_LOGGING = os.environ.get("UNSLOTH_ENABLE_LOGGING", "0") in (
@@ -1371,6 +1372,88 @@ def disable_broken_wandb():
         os.environ["WANDB_DISABLED"] = "true"
 
 
+def patch_peft_weight_converter_compatibility():
+    """Allow PEFT converter rebuilds on legacy converter constructors."""
+    try:
+        from peft.utils import transformers_weight_conversion as twc
+    except (ImportError, AttributeError):
+        return
+
+    if getattr(twc, "_unsloth_weight_converter_compat_patch", False):
+        return
+
+    import threading
+
+    original_build = twc.build_peft_weight_mapping
+    patch_lock = threading.RLock()
+
+    def _patch_weight_converter_ctors(weight_conversions, patched):
+        seen_classes = set()
+
+        for conversion in weight_conversions:
+            conversion_cls = conversion.__class__
+            if conversion_cls in seen_classes:
+                continue
+            seen_classes.add(conversion_cls)
+
+            original_init = conversion_cls.__init__
+            params = inspect.signature(original_init).parameters
+            supports_kwargs = any(
+                p.kind == inspect.Parameter.VAR_KEYWORD for p in params.values()
+            )
+            supports_distributed = "distributed_operation" in params
+            supports_quantization = "quantization_operation" in params
+            if supports_kwargs or (supports_distributed and supports_quantization):
+                continue
+
+            def _compat_init(
+                self,
+                *args,
+                __original_init = original_init,
+                __supports_distributed = supports_distributed,
+                __supports_quantization = supports_quantization,
+                **kwargs,
+            ):
+                unsupported = {}
+                if not __supports_distributed and "distributed_operation" in kwargs:
+                    unsupported["distributed_operation"] = kwargs.pop(
+                        "distributed_operation"
+                    )
+                if not __supports_quantization and "quantization_operation" in kwargs:
+                    unsupported["quantization_operation"] = kwargs.pop(
+                        "quantization_operation"
+                    )
+                result = __original_init(self, *args, **kwargs)
+                for name, value in unsupported.items():
+                    if hasattr(self, name):
+                        setattr(self, name, value)
+                return result
+
+            conversion_cls.__init__ = _compat_init
+            patched.append((conversion_cls, original_init))
+
+    @functools.wraps(original_build)
+    def _build_peft_weight_mapping_compat(
+        weight_conversions,
+        adapter_name,
+        peft_config = None,
+    ):
+        if not weight_conversions:
+            return original_build(weight_conversions, adapter_name, peft_config)
+
+        patched_classes = []
+        with patch_lock:
+            try:
+                _patch_weight_converter_ctors(weight_conversions, patched_classes)
+                return original_build(weight_conversions, adapter_name, peft_config)
+            finally:
+                for conversion_cls, original_init in patched_classes:
+                    conversion_cls.__init__ = original_init
+
+    twc.build_peft_weight_mapping = _build_peft_weight_mapping_compat
+    twc._unsloth_weight_converter_compat_patch = True
+
+
 CAUSAL_CONV1D_BROKEN = False
 _CAUSAL_CONV1D_PREFIX = "causal_conv1d"
 _CAUSAL_CONV1D_BLOCKER_SENTINEL = "_unsloth_causal_conv1d_blocker"