diff --git a/milli/src/update/words_prefix_integer_docids.rs b/milli/src/update/words_prefix_integer_docids.rs
index c65438928..e083f510a 100644
--- a/milli/src/update/words_prefix_integer_docids.rs
+++ b/milli/src/update/words_prefix_integer_docids.rs
@@ -9,9 +9,11 @@ use log::debug;
 use crate::error::SerializationError;
 use crate::heed_codec::StrBEU16Codec;
 use crate::index::main_key::WORDS_PREFIXES_FST_KEY;
+use crate::update::del_add::{deladd_serialize_add_side, DelAdd, KvWriterDelAdd};
 use crate::update::index_documents::{
-    create_sorter, merge_cbo_roaring_bitmaps, sorter_into_lmdb_database, valid_lmdb_key,
-    CursorClonableMmap, MergeFn,
+    create_sorter, merge_deladd_cbo_roaring_bitmaps,
+    merge_deladd_cbo_roaring_bitmaps_into_cbo_roaring_bitmap, valid_lmdb_key,
+    write_sorter_into_database, CursorClonableMmap, MergeFn,
 };
 use crate::{CboRoaringBitmapCodec, Result};
 
@@ -55,7 +57,7 @@ impl<'t, 'u, 'i> WordPrefixIntegerDocids<'t, 'u, 'i> {
 
         let mut prefix_integer_docids_sorter = create_sorter(
             grenad::SortAlgorithm::Unstable,
-            merge_cbo_roaring_bitmaps,
+            merge_deladd_cbo_roaring_bitmaps,
             self.chunk_compression_type,
             self.chunk_compression_level,
             self.max_nb_chunks,
@@ -108,6 +110,7 @@ impl<'t, 'u, 'i> WordPrefixIntegerDocids<'t, 'u, 'i> {
 
         // We fetch the docids associated to the newly added word prefix fst only.
         let db = self.word_database.remap_data_type::<ByteSlice>();
+        let mut buffer = Vec::new();
         for prefix_bytes in new_prefix_fst_words {
             let prefix = str::from_utf8(prefix_bytes.as_bytes()).map_err(|_| {
                 SerializationError::Decoding { db_name: Some(WORDS_PREFIXES_FST_KEY) }
@@ -123,7 +126,11 @@ impl<'t, 'u, 'i> WordPrefixIntegerDocids<'t, 'u, 'i> {
                 if word.starts_with(prefix) {
                     let key = (prefix, pos);
                     let bytes = StrBEU16Codec::bytes_encode(&key).unwrap();
-                    prefix_integer_docids_sorter.insert(bytes, data)?;
+
+                    buffer.clear();
+                    let mut writer = KvWriterDelAdd::new(&mut buffer);
+                    writer.insert(DelAdd::Addition, data)?;
+                    prefix_integer_docids_sorter.insert(bytes, writer.into_inner()?)?;
                 }
             }
         }
@@ -143,12 +150,16 @@ impl<'t, 'u, 'i> WordPrefixIntegerDocids<'t, 'u, 'i> {
             drop(iter);
         }
 
+        let database_is_empty = self.prefix_database.is_empty(self.wtxn)?;
+
         // We finally write all the word prefix integer docids into the LMDB database.
-        sorter_into_lmdb_database(
-            self.wtxn,
-            *self.prefix_database.as_polymorph(),
+        write_sorter_into_database(
             prefix_integer_docids_sorter,
-            merge_cbo_roaring_bitmaps,
+            &self.prefix_database,
+            self.wtxn,
+            database_is_empty,
+            deladd_serialize_add_side,
+            merge_deladd_cbo_roaring_bitmaps_into_cbo_roaring_bitmap,
         )?;
 
         Ok(())
@@ -159,6 +170,7 @@ fn write_prefixes_in_sorter(
     prefixes: &mut HashMap<Vec<u8>, Vec<Vec<u8>>>,
     sorter: &mut grenad::Sorter<MergeFn>,
 ) -> Result<()> {
+    // TODO: Merge before insertion.
     for (key, data_slices) in prefixes.drain() {
         for data in data_slices {
             if valid_lmdb_key(&key) {