diff --git a/milli/src/update/index_documents/extract/extract_docid_word_positions.rs b/milli/src/update/index_documents/extract/extract_docid_word_positions.rs
index 716e4dd6b..b1e6f24be 100644
--- a/milli/src/update/index_documents/extract/extract_docid_word_positions.rs
+++ b/milli/src/update/index_documents/extract/extract_docid_word_positions.rs
@@ -40,6 +40,7 @@ pub fn extract_docid_word_positions<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory,
+        true,
     );
 
     // initialize buffers.
diff --git a/milli/src/update/index_documents/extract/extract_facet_number_docids.rs b/milli/src/update/index_documents/extract/extract_facet_number_docids.rs
index 8a5a93270..34bece989 100644
--- a/milli/src/update/index_documents/extract/extract_facet_number_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_facet_number_docids.rs
@@ -32,6 +32,7 @@ pub fn extract_facet_number_docids<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory,
+        true,
     );
 
     let mut buffer = Vec::new();
diff --git a/milli/src/update/index_documents/extract/extract_facet_string_docids.rs b/milli/src/update/index_documents/extract/extract_facet_string_docids.rs
index f7bdcbb56..e0d7e1386 100644
--- a/milli/src/update/index_documents/extract/extract_facet_string_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_facet_string_docids.rs
@@ -61,6 +61,7 @@ fn extract_facet_string_docids_document_update<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 2),
+        true,
     );
 
     let mut normalized_facet_string_docids_sorter = create_sorter(
@@ -70,6 +71,7 @@ fn extract_facet_string_docids_document_update<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 2),
+        true,
     );
 
     let mut buffer = Vec::new();
@@ -149,6 +151,7 @@ fn extract_facet_string_docids_settings<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 2),
+        true,
     );
 
     let mut normalized_facet_string_docids_sorter = create_sorter(
@@ -158,6 +161,7 @@ fn extract_facet_string_docids_settings<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 2),
+        true,
     );
 
     let mut buffer = Vec::new();
diff --git a/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs b/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
index f7f447ca9..047669521 100644
--- a/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
+++ b/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
@@ -53,6 +53,7 @@ pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 2),
+        true,
     );
 
     let mut fid_docid_facet_strings_sorter = create_sorter(
@@ -62,6 +63,7 @@ pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 2),
+        true,
     );
 
     // The tuples represents the Del and Add side for a bitmap
diff --git a/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs b/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs
index 784de5d94..5739a5e15 100644
--- a/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_fid_word_count_docids.rs
@@ -35,6 +35,7 @@ pub fn extract_fid_word_count_docids<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory,
+        true,
     );
 
     let mut key_buffer = Vec::new();
diff --git a/milli/src/update/index_documents/extract/extract_word_docids.rs b/milli/src/update/index_documents/extract/extract_word_docids.rs
index 70db9d759..829da768c 100644
--- a/milli/src/update/index_documents/extract/extract_word_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_word_docids.rs
@@ -44,6 +44,7 @@ pub fn extract_word_docids<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 3),
+        true,
     );
     let mut key_buffer = Vec::new();
     let mut del_words = BTreeSet::new();
@@ -98,6 +99,7 @@ pub fn extract_word_docids<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 3),
+        true,
     );
 
     let mut exact_word_docids_sorter = create_sorter(
@@ -107,6 +109,7 @@ pub fn extract_word_docids<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory.map(|m| m / 3),
+        true,
     );
 
     let mut iter = word_fid_docids_sorter.into_stream_merger_iter()?;
diff --git a/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs b/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs
index 705a5c96f..6194da23d 100644
--- a/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_word_pair_proximity_docids.rs
@@ -49,6 +49,7 @@ pub fn extract_word_pair_proximity_docids<R: io::Read + io::Seek>(
                 indexer.chunk_compression_level,
                 indexer.max_nb_chunks,
                 max_memory.map(|m| m / MAX_DISTANCE as usize),
+                true,
             )
         })
         .collect();
diff --git a/milli/src/update/index_documents/extract/extract_word_position_docids.rs b/milli/src/update/index_documents/extract/extract_word_position_docids.rs
index bee510bfb..f870fbe1b 100644
--- a/milli/src/update/index_documents/extract/extract_word_position_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_word_position_docids.rs
@@ -33,6 +33,7 @@ pub fn extract_word_position_docids<R: io::Read + io::Seek>(
         indexer.chunk_compression_level,
         indexer.max_nb_chunks,
         max_memory,
+        true,
     );
 
     let mut del_word_positions: BTreeSet<(u16, Vec<u8>)> = BTreeSet::new();
diff --git a/milli/src/update/index_documents/helpers/grenad_helpers.rs b/milli/src/update/index_documents/helpers/grenad_helpers.rs
index 1f8f7eddf..220567208 100644
--- a/milli/src/update/index_documents/helpers/grenad_helpers.rs
+++ b/milli/src/update/index_documents/helpers/grenad_helpers.rs
@@ -37,6 +37,7 @@ pub fn create_sorter<MF: MergeFunction>(
     chunk_compression_level: Option<u32>,
     max_nb_chunks: Option<usize>,
     max_memory: Option<usize>,
+    sort_in_parallel: bool,
 ) -> grenad::Sorter<MF> {
     let mut builder = grenad::Sorter::builder(merge);
     builder.chunk_compression_type(chunk_compression_type);
@@ -51,7 +52,7 @@ pub fn create_sorter<MF: MergeFunction>(
         builder.allow_realloc(false);
     }
     builder.sort_algorithm(sort_algorithm);
-    builder.sort_in_parallel(true);
+    builder.sort_in_parallel(sort_in_parallel);
     builder.build()
 }
 
diff --git a/milli/src/update/index_documents/transform.rs b/milli/src/update/index_documents/transform.rs
index 65007aa32..84135ff24 100644
--- a/milli/src/update/index_documents/transform.rs
+++ b/milli/src/update/index_documents/transform.rs
@@ -127,6 +127,7 @@ impl<'a, 'i> Transform<'a, 'i> {
             indexer_settings.chunk_compression_level,
             indexer_settings.max_nb_chunks,
             indexer_settings.max_memory.map(|mem| mem / 2),
+            true,
         );
 
         // We initialize the sorter with the user indexing settings.
@@ -137,6 +138,7 @@ impl<'a, 'i> Transform<'a, 'i> {
             indexer_settings.chunk_compression_level,
             indexer_settings.max_nb_chunks,
             indexer_settings.max_memory.map(|mem| mem / 2),
+            true,
         );
         let documents_ids = index.documents_ids(wtxn)?;
 
@@ -988,6 +990,7 @@ impl<'a, 'i> Transform<'a, 'i> {
                 self.indexer_settings.chunk_compression_level,
                 self.indexer_settings.max_nb_chunks,
                 self.indexer_settings.max_memory.map(|mem| mem / 2),
+                true,
             ))
         } else {
             None
@@ -1030,6 +1033,7 @@ impl<'a, 'i> Transform<'a, 'i> {
                     self.indexer_settings.chunk_compression_level,
                     self.indexer_settings.max_nb_chunks,
                     self.indexer_settings.max_memory.map(|mem| mem / 2),
+                    true,
                 ))
             } else {
                 None
diff --git a/milli/src/update/new/extract/faceted/extract_facets.rs b/milli/src/update/new/extract/faceted/extract_facets.rs
index 82f80c7b5..9f3ed18d8 100644
--- a/milli/src/update/new/extract/faceted/extract_facets.rs
+++ b/milli/src/update/new/extract/faceted/extract_facets.rs
@@ -46,6 +46,10 @@ impl<'extractor> Extractor<'extractor> for FacetedExtractorData<'extractor> {
                 self.grenad_parameters.chunk_compression_level,
                 self.grenad_parameters.max_nb_chunks,
                 self.max_memory,
+                // *NOTE*: this must not be set to true:
+                // 1. we're already using max parallelism in the pool, so it wouldn't help
+                // 2. it creates correctness issues if it causes to yield a borrow-mut wielding task
+                false,
             ),
         ))))
     }
diff --git a/milli/src/update/new/extract/searchable/extract_word_docids.rs b/milli/src/update/new/extract/searchable/extract_word_docids.rs
index 5d70408bb..c76ab49d0 100644
--- a/milli/src/update/new/extract/searchable/extract_word_docids.rs
+++ b/milli/src/update/new/extract/searchable/extract_word_docids.rs
@@ -48,6 +48,7 @@ impl WordDocidsCachedSorters {
                 indexer.chunk_compression_level,
                 indexer.max_nb_chunks,
                 max_memory,
+                false,
             ),
         );
         let word_docids = CboCachedSorter::new(
@@ -59,6 +60,7 @@ impl WordDocidsCachedSorters {
                 indexer.chunk_compression_level,
                 indexer.max_nb_chunks,
                 max_memory,
+                false,
             ),
         );
         let exact_word_docids = CboCachedSorter::new(
@@ -70,6 +72,7 @@ impl WordDocidsCachedSorters {
                 indexer.chunk_compression_level,
                 indexer.max_nb_chunks,
                 max_memory,
+                false,
             ),
         );
         let word_position_docids = CboCachedSorter::new(
@@ -81,6 +84,7 @@ impl WordDocidsCachedSorters {
                 indexer.chunk_compression_level,
                 indexer.max_nb_chunks,
                 max_memory,
+                false,
             ),
         );
         let fid_word_count_docids = CboCachedSorter::new(
@@ -92,6 +96,7 @@ impl WordDocidsCachedSorters {
                 indexer.chunk_compression_level,
                 indexer.max_nb_chunks,
                 max_memory,
+                false,
             ),
         );
 
diff --git a/milli/src/update/new/extract/searchable/mod.rs b/milli/src/update/new/extract/searchable/mod.rs
index 1edeec8b4..8934ee892 100644
--- a/milli/src/update/new/extract/searchable/mod.rs
+++ b/milli/src/update/new/extract/searchable/mod.rs
@@ -50,6 +50,7 @@ impl<'extractor, EX: SearchableExtractor + Sync> Extractor<'extractor>
                 self.grenad_parameters.chunk_compression_level,
                 self.grenad_parameters.max_nb_chunks,
                 self.max_memory,
+                false,
             ),
         ))))
     }
diff --git a/milli/src/update/word_prefix_docids.rs b/milli/src/update/word_prefix_docids.rs
index f683146cf..d129d485e 100644
--- a/milli/src/update/word_prefix_docids.rs
+++ b/milli/src/update/word_prefix_docids.rs
@@ -60,6 +60,7 @@ impl<'t, 'i> WordPrefixDocids<'t, 'i> {
             self.chunk_compression_level,
             self.max_nb_chunks,
             self.max_memory,
+            true,
         );
 
         if !common_prefix_fst_words.is_empty() {
diff --git a/milli/src/update/words_prefix_integer_docids.rs b/milli/src/update/words_prefix_integer_docids.rs
index 28b9b1523..ff974b797 100644
--- a/milli/src/update/words_prefix_integer_docids.rs
+++ b/milli/src/update/words_prefix_integer_docids.rs
@@ -65,6 +65,7 @@ impl<'t, 'i> WordPrefixIntegerDocids<'t, 'i> {
             self.chunk_compression_level,
             self.max_nb_chunks,
             self.max_memory,
+            true,
         );
 
         if !common_prefix_fst_words.is_empty() {