diff --git a/bitsandbytes/autograd/_functions.py b/bitsandbytes/autograd/_functions.py
index 91eec4a..c3c2bf8 100644
--- a/bitsandbytes/autograd/_functions.py
+++ b/bitsandbytes/autograd/_functions.py
@@ -321,6 +321,7 @@ class MatMul8bitLt(torch.autograd.Function):
 
         # 4. Mixed-precision decomposition matmul
         if coo_tensorA is not None and subA is not None:
+            assert subA.dtype == state.subB.dtype, (subA.dtype, state.subB.dtype)
             output += torch.matmul(subA, state.subB)
 
         # 5. Save state