diff --git a/moondream/torch/config.py b/moondream/torch/config.py
index ef3f7875..acfe7e02 100644
--- a/moondream/torch/config.py
+++ b/moondream/torch/config.py
@@ -9,6 +9,7 @@ class TextConfig:
     vocab_size: int = 51200
     max_context: int = 2048
     n_heads: int = 32
+    prefix_attn: int = 730
 
 
 @dataclass(frozen=True)
diff --git a/moondream/torch/text.py b/moondream/torch/text.py
index d370d871..744e62f2 100644
--- a/moondream/torch/text.py
+++ b/moondream/torch/text.py
@@ -160,7 +160,8 @@ def build_text_model(config: TextConfig, dtype: torch.dtype) -> nn.Module:
     attn_mask = torch.tril(
         torch.ones(1, 1, config.max_context, config.max_context, dtype=torch.bool)
     )
-    attn_mask[..., :730, :730] = 1
+    if config.prefix_attn != 0:
+        attn_mask[..., : config.prefix_attn, : config.prefix_attn] = 1
     text.register_buffer("attn_mask", attn_mask, persistent=False)
 
     return text