diff --git a/backend/alembic/versions/8f43500ee275_add_index.py b/backend/alembic/versions/8f43500ee275_add_index.py
index 7ef2e007d..a29357924 100644
--- a/backend/alembic/versions/8f43500ee275_add_index.py
+++ b/backend/alembic/versions/8f43500ee275_add_index.py
@@ -17,11 +17,11 @@ depends_on = None
 
 def upgrade() -> None:
     # Create a basic index on the lowercase message column for direct text matching
-    # Limit to 2000 characters to stay well under the 8191 byte limit
+    # Limit to 1500 characters to stay well under the 2856 byte limit of btree version 4
     op.execute(
         """
         CREATE INDEX idx_chat_message_message_lower
-        ON chat_message (LOWER(substring(message, 1, 2000)))
+        ON chat_message (LOWER(substring(message, 1, 1500)))
         """
     )