From 4d878fa33738900b1f81fac0217b71439be904be Mon Sep 17 00:00:00 2001
From: ailuntz <ailuntz@icloud.com>
Date: Tue, 10 Mar 2026 16:11:10 +0800
Subject: [PATCH] Guard SCB access in Linear8bitLt

---
 bitsandbytes/nn/modules.py | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/bitsandbytes/nn/modules.py b/bitsandbytes/nn/modules.py
index ff8ce9c3d..11dc13e37 100644
--- a/bitsandbytes/nn/modules.py
+++ b/bitsandbytes/nn/modules.py
@@ -1054,7 +1054,7 @@ def _save_to_state_dict(self, destination, prefix, keep_vars):
         scb_name = "SCB"
 
         # case 1: .cuda was called, SCB is in self.weight
-        param_from_weight = getattr(self.weight, scb_name)
+        param_from_weight = getattr(self.weight, scb_name, None)
         # case 2: self.init_8bit_state was called, SCB is in self.state
         param_from_state = getattr(self.state, scb_name)
 
@@ -1095,7 +1095,8 @@ def _load_from_state_dict(
         for key in unexpected_copy:
             input_name = key[len(prefix) :]
             if input_name == "SCB":
-                if self.weight.SCB is None:
+                weight_scb = getattr(self.weight, "SCB", None)
+                if weight_scb is None:
                     # buffers not yet initialized, can't access them directly without quantizing first
                     raise RuntimeError(
                         "Loading a quantized checkpoint into non-quantized Linear8bitLt is "
@@ -1103,7 +1104,7 @@ def _load_from_state_dict(
                     )
 
                 input_param = state_dict[key]
-                self.weight.SCB.copy_(input_param)
+                weight_scb.copy_(input_param)
 
                 if self.state.SCB is not None:
                     self.state.SCB = self.weight.SCB
@@ -1133,7 +1134,7 @@ def to(self, *args, **kwargs):
 
     def forward(self, x: torch.Tensor):
         self.state.is_training = self.training
-        if self.weight.CB is not None:
+        if getattr(self.weight, "CB", None) is not None:
             self.init_8bit_state()
 
         # weights are cast automatically as Int8Params, but the bias has to be cast manually
@@ -1142,7 +1143,7 @@ def forward(self, x: torch.Tensor):
 
         out = bnb.matmul(x, self.weight, bias=self.bias, state=self.state)
 
-        if not self.state.has_fp16_weights and self.state.CB is not None:
+        if not self.state.has_fp16_weights and self.state.CB is not None and hasattr(self.weight, "CB"):
             self.weight.data = self.state.CB
 
         return out