diff --git a/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs b/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs
index 79b52695e..117da1308 100644
--- a/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs
+++ b/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs
@@ -6,6 +6,7 @@ use byteorder::{NativeEndian, ReadBytesExt, WriteBytesExt};
 use roaring::RoaringBitmap;
 
 use crate::heed_codec::BytesDecodeOwned;
+use crate::update::del_add::{DelAdd, KvReaderDelAdd};
 
 /// This is the limit where using a byteorder became less size efficient
 /// than using a direct roaring encoding, it is also the point where we are able
@@ -99,6 +100,28 @@ impl CboRoaringBitmapCodec {
 
         Ok(())
     }
+
+    /// Merges a DelAdd delta into a CboRoaringBitmap.
+    pub fn merge_deladd_into(
+        deladd: KvReaderDelAdd<'_>,
+        previous: &[u8],
+        buffer: &mut Vec<u8>,
+    ) -> io::Result<()> {
+        // Deserialize the bitmap that is already there
+        let mut previous = Self::deserialize_from(previous)?;
+
+        // Remove integers we no more want in the previous bitmap
+        if let Some(value) = deladd.get(DelAdd::Deletion) {
+            previous -= Self::deserialize_from(value)?;
+        }
+
+        // Insert the new integers we want in the previous bitmap
+        if let Some(value) = deladd.get(DelAdd::Addition) {
+            previous |= Self::deserialize_from(value)?;
+        }
+
+        previous.serialize_into(buffer)
+    }
 }
 
 impl heed::BytesDecode<'_> for CboRoaringBitmapCodec {
diff --git a/milli/src/update/index_documents/typed_chunk.rs b/milli/src/update/index_documents/typed_chunk.rs
index e0e2ff1ec..faeee944f 100644
--- a/milli/src/update/index_documents/typed_chunk.rs
+++ b/milli/src/update/index_documents/typed_chunk.rs
@@ -134,7 +134,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
             is_merged_database = true;
         }
@@ -153,7 +153,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
 
             let exact_word_docids_iter = unsafe { as_cloneable_grenad(&exact_word_docids_reader) }?;
@@ -163,7 +163,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
 
             let word_fid_docids_iter = unsafe { as_cloneable_grenad(&word_fid_docids_reader) }?;
@@ -173,7 +173,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
 
             // create fst from word docids
@@ -195,7 +195,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
             is_merged_database = true;
         }
@@ -216,7 +216,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
             is_merged_database = true;
         }
@@ -227,7 +227,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
             is_merged_database = true;
         }
@@ -238,7 +238,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
             is_merged_database = true;
         }
@@ -249,7 +249,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 wtxn,
                 index_is_empty,
                 deladd_serialize_add_side,
-                merge_cbo_roaring_bitmaps,
+                merge_deladd_cbo_roaring_bitmaps,
             )?;
             is_merged_database = true;
         }
@@ -388,17 +388,6 @@ fn merge_word_docids_reader_into_fst(
     Ok(builder.into_set())
 }
 
-fn merge_cbo_roaring_bitmaps(
-    new_value: &[u8],
-    db_value: &[u8],
-    buffer: &mut Vec<u8>,
-) -> Result<()> {
-    Ok(CboRoaringBitmapCodec::merge_into(
-        &[Cow::Borrowed(db_value), Cow::Borrowed(new_value)],
-        buffer,
-    )?)
-}
-
 /// A function that extracts and returns the Add side of a DelAdd obkv.
 /// This is useful when there are no previous value in the database and
 /// therefore we don't need to do a diff with what's already there.
@@ -409,6 +398,22 @@ fn deladd_serialize_add_side<'a>(obkv: &'a [u8], _buffer: &mut Vec<u8>) -> Resul
     Ok(KvReaderDelAdd::new(obkv).get(DelAdd::Addition).unwrap_or_default())
 }
 
+/// A function that merges a DelAdd of bitmao into an already existing bitmap.
+///
+/// The first argument is the DelAdd obkv of CboRoaringBitmaps and
+/// the second one is the CboRoaringBitmap to merge into.
+fn merge_deladd_cbo_roaring_bitmaps(
+    deladd_obkv: &[u8],
+    previous: &[u8],
+    buffer: &mut Vec<u8>,
+) -> Result<()> {
+    Ok(CboRoaringBitmapCodec::merge_deladd_into(
+        KvReaderDelAdd::new(deladd_obkv),
+        previous,
+        buffer,
+    )?)
+}
+
 /// Write provided entries in database using serialize_value function.
 /// merge_values function is used if an entry already exist in the database.
 fn write_entries_into_database<R, K, V, FS, FM>(