diff --git a/pageserver/src/tenant/blob_io.rs b/pageserver/src/tenant/blob_io.rs
index 24b4e4f3eaae..2be8816cefbd 100644
--- a/pageserver/src/tenant/blob_io.rs
+++ b/pageserver/src/tenant/blob_io.rs
@@ -238,10 +238,13 @@ impl<const BUFFERED: bool> BlobWriter<BUFFERED> {
                         io_buf,
                         Err(Error::new(
                             ErrorKind::Other,
-                            format!("blob too large ({} bytes)", len),
+                            format!("blob too large ({len} bytes)"),
                         )),
                     );
                 }
+                if len > 0x0fff_ffff {
+                    tracing::warn!("writing blob above future limit ({len} bytes)");
+                }
                 let mut len_buf = (len as u32).to_be_bytes();
                 len_buf[0] |= 0x80;
                 io_buf.extend_from_slice(&len_buf[..]);