diff --git a/server/text_generation_server/utils/flash_attn.py b/server/text_generation_server/utils/flash_attn.py
index caf072b7..8f0fcee6 100644
--- a/server/text_generation_server/utils/flash_attn.py
+++ b/server/text_generation_server/utils/flash_attn.py
@@ -80,7 +80,7 @@ def attention(
         )
 
     if HAS_FLASH_ATTN:
-        if window_size_left != 0:
+        if window_size_left != -1:
             raise NotImplementedError(
                 "window_size_left is only available with flash attn v2"
             )