diff --git a/milli/src/update/index_documents/helpers/mod.rs b/milli/src/update/index_documents/helpers/mod.rs
index 3f38d4f25..128288982 100644
--- a/milli/src/update/index_documents/helpers/mod.rs
+++ b/milli/src/update/index_documents/helpers/mod.rs
@@ -17,7 +17,7 @@ pub use merge_functions::{
 };
 
 pub fn valid_lmdb_key(key: impl AsRef<[u8]>) -> bool {
-    key.as_ref().len() <= 511
+    key.as_ref().len() <= 511 && !key.as_ref().is_empty()
 }
 
 /// Divides one slice into two at an index, returns `None` if mid is out of bounds.