diff --git a/xformers/components/attention/blocksparse.py b/xformers/components/attention/blocksparse.py
index a9b701ce4e..d6302e8e4a 100644
--- a/xformers/components/attention/blocksparse.py
+++ b/xformers/components/attention/blocksparse.py
@@ -13,6 +13,7 @@
 from torch import nn
 
 from xformers.components.attention import Attention, AttentionConfig, register_attention
+from xformers.components.attention.utils import bool_mask_to_additive
 
 _mask_type_warning = True
 
@@ -119,10 +120,9 @@ def update_mask_type(self, mask: torch.Tensor, to_dtype: torch.dtype):
             global _mask_type_warning
             if _mask_type_warning:
                 logging.warning(
-                    "Mask has to be multiplicative. Fixing that but this slows things down"
+                    "Mask has to be additive. Fixing that but this slows things down"
                 )
-                _mask_type_warning = False  # Only warn once
-            mask = mask.to(to_dtype)
+            mask = bool_mask_to_additive(mask)
 
         def forward(
             self,
@@ -136,11 +136,10 @@ def forward(
             **kwargs,
         ) -> torch.Tensor:
             r"""
-            att_mask            A 2D attention mask. The dtype must be the same as q. Multiplicative mask where a value
-                                of 1 will keep the value, while a value of 0 will mask the value.
+            att_mask            A 2D attention mask. The dtype must be the same as q. An additive mask is expected,
+                                meaning float values using "-inf" to mask values.
             key_padding_mask    A mask with size (batch size x sequence length). The dtype must be the same as q.
-                                Multiplicative mask where a value of 1 will keep the value, while a value of 0 will
-                                mask the value.
+                                An additive mask is expected, meaning float values using "-inf" to mask values
             """
 
             # NOTE:
@@ -149,9 +148,9 @@ def forward(
             # If blocks are to be constantly masked, better perf would thus be reached by signalling them out in the
             # initial attention setup
 
-            if att_mask is not None and att_mask.dtype != q.dtype:
+            if att_mask is not None and att_mask.dtype == torch.bool:
                 self.update_mask_type(att_mask, q.dtype)
-            if key_padding_mask is not None and key_padding_mask.dtype != q.dtype:
+            if key_padding_mask is not None and key_padding_mask.dtype == torch.bool:
                 self.update_mask_type(key_padding_mask, q.dtype)
 
             assert (
@@ -197,8 +196,8 @@ def forward(
                 scale=scale,
                 key_padding_mask=key_padding_mask,
                 attn_mask=att_mask,
-                key_padding_mask_mode=MaskType.MUL,
-                attn_mask_mode=MaskType.MUL,
+                key_padding_mask_mode=MaskType.ADD,
+                attn_mask_mode=MaskType.ADD,
             )
 
             # - then (dense) attention is (sparse) attention matrix * dense (value)