diff --git a/meilisearch-core/src/update/documents_addition.rs b/meilisearch-core/src/update/documents_addition.rs
index a4b41d2a8..5603966b0 100644
--- a/meilisearch-core/src/update/documents_addition.rs
+++ b/meilisearch-core/src/update/documents_addition.rs
@@ -171,15 +171,23 @@ pub fn apply_addition<'a, 'b>(
     let mut new_internal_docids = Vec::with_capacity(new_documents.len());
 
     for mut document in new_documents {
+        let external_docids_get = |docid: &str| {
+            match (external_docids.get(docid), new_external_docids.get(docid)) {
+                (_, Some(&id))
+                | (Some(id), _) => Some(id as u32),
+                (None, None) => None,
+            }
+        };
+
         let (internal_docid, external_docid) =
             extract_document_id(
                 &primary_key,
                 &document,
-                &external_docids,
+                &external_docids_get,
                 &mut available_ids,
             )?;
 
-        new_external_docids.insert(external_docid, internal_docid.0);
+        new_external_docids.insert(external_docid, internal_docid.0 as u64);
         new_internal_docids.push(internal_docid);
 
         if partial {
diff --git a/meilisearch-core/src/update/helpers.rs b/meilisearch-core/src/update/helpers.rs
index 6e8902182..1942c322c 100644
--- a/meilisearch-core/src/update/helpers.rs
+++ b/meilisearch-core/src/update/helpers.rs
@@ -98,15 +98,17 @@ pub fn value_to_number(value: &Value) -> Option<Number> {
 
 /// Validates a string representation to be a correct document id and returns
 /// the corresponding id or generate a new one, this is the way we produce documents ids.
-pub fn discover_document_id(
+pub fn discover_document_id<F>(
     docid: &str,
-    external_docids: &FstMapCow,
+    external_docids_get: F,
     available_docids: &mut DiscoverIds<'_>,
 ) -> Result<DocumentId, SerializerError>
+where
+    F: FnOnce(&str) -> Option<u32>
 {
     if docid.chars().all(|x| x.is_ascii_alphanumeric() || x == '-' || x == '_') {
-        match external_docids.get(docid) {
-            Some(id) => Ok(DocumentId(id as u32)),
+        match external_docids_get(docid) {
+            Some(id) => Ok(DocumentId(id)),
             None => {
                 let internal_id = available_docids.next().expect("no more ids available");
                 Ok(internal_id)
@@ -118,12 +120,14 @@ pub fn discover_document_id(
 }
 
 /// Extracts and validates the document id of a document.
-pub fn extract_document_id(
+pub fn extract_document_id<F>(
     primary_key: &str,
     document: &IndexMap<String, Value>,
-    external_docids: &FstMapCow,
+    external_docids_get: F,
     available_docids: &mut DiscoverIds<'_>,
 ) -> Result<(DocumentId, String), SerializerError>
+where
+    F: FnOnce(&str) -> Option<u32>
 {
     match document.get(primary_key) {
         Some(value) => {
@@ -132,7 +136,7 @@ pub fn extract_document_id(
                 Value::String(string) => string.clone(),
                 _ => return Err(SerializerError::InvalidDocumentIdFormat),
             };
-            discover_document_id(&docid, external_docids, available_docids).map(|id| (id, docid))
+            discover_document_id(&docid, external_docids_get, available_docids).map(|id| (id, docid))
         }
         None => Err(SerializerError::DocumentIdNotFound),
     }