diff --git a/bitsandbytes/functional.py b/bitsandbytes/functional.py
index a461d1749..3e90364bb 100644
--- a/bitsandbytes/functional.py
+++ b/bitsandbytes/functional.py
@@ -890,7 +890,16 @@ def quantize_fp4(A: Tensor, absmax: Tensor = None, out: Tensor = None, blocksize
 def quantize_nf4(A: Tensor, absmax: Tensor = None, out: Tensor = None, blocksize=64, compress_statistics=False, quant_storage=torch.uint8):
     return quantize_4bit(A, absmax, out, blocksize, compress_statistics, 'nf4', quant_storage)
 
-def quantize_4bit(A: Tensor, absmax: Tensor = None, out: Tensor = None, blocksize=64, compress_statistics=False, quant_type='fp4', quant_storage=torch.uint8) -> (Tensor, QuantState):
+
+def quantize_4bit(
+    A: Tensor,
+    absmax: Tensor = None,
+    out: Tensor = None,
+    blocksize=64,
+    compress_statistics=False,
+    quant_type='fp4',
+    quant_storage=torch.uint8,
+) -> Tuple[Tensor, QuantState]:
     """
     Quantize tensor A in blocks of 4-bit values.