diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2f4f2c168..3cfee1483 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,7 +14,7 @@
   - Fix setting consistency bug (#1128)
   - Fix attributes to retrieve bug (#1131)
   - Increase default payload size (#1147)
-  - Improvements to code quality (#1167, #1165, #1126, #1161)
+  - Improvements to code quality (#1167, #1165, #1126, #1151)
 
 ## v0.17.0 - 2020-11-30
   - Fix corrupted data during placeholder search (#1089)
diff --git a/meilisearch-core/src/update/settings_update.rs b/meilisearch-core/src/update/settings_update.rs
index e96d5702c..c9d40fa1b 100644
--- a/meilisearch-core/src/update/settings_update.rs
+++ b/meilisearch-core/src/update/settings_update.rs
@@ -1,7 +1,7 @@
 use std::{borrow::Cow, collections::{BTreeMap, BTreeSet}};
 
 use heed::Result as ZResult;
-use fst::{set::OpBuilder, SetBuilder};
+use fst::{SetBuilder, set::OpBuilder};
 use sdset::SetBuf;
 use meilisearch_schema::Schema;
 use meilisearch_tokenizer::analyzer::{Analyzer, AnalyzerConfig};
@@ -298,16 +298,23 @@ pub fn apply_synonyms_update(
             .tokens()
             .fold(String::new(), |s, t| s + t.text())
     }
+    
+    // normalize synonyms and reorder them creating a BTreeMap
+    let synonyms: BTreeMap<String, Vec<String>> = synonyms.into_iter().map( |(word, alternatives)| {
+        let word = normalize(&analyzer, &word);
+        let alternatives = alternatives.into_iter().map(|text| normalize(&analyzer, &text)).collect();
 
+        (word, alternatives)
+    }).collect();
+
+    // index synonyms,
+    // synyonyms have to be ordered by key before indexation
     let mut synonyms_builder = SetBuilder::memory();
     synonyms_store.clear(writer)?;
     for (word, alternatives) in synonyms {
-        let word = normalize(&analyzer, &word);
-
         synonyms_builder.insert(&word)?;
 
         let alternatives = {
-            let alternatives = alternatives.iter().map(|text| normalize(&analyzer, &text)).collect();
             let alternatives = SetBuf::from_dirty(alternatives);
             let mut alternatives_builder = SetBuilder::memory();
             alternatives_builder.extend_iter(alternatives)?;
diff --git a/meilisearch-http/src/routes/document.rs b/meilisearch-http/src/routes/document.rs
index e529839c7..202575cc3 100644
--- a/meilisearch-http/src/routes/document.rs
+++ b/meilisearch-http/src/routes/document.rs
@@ -175,7 +175,6 @@ async fn update_multiple_documents(
             .ok_or(meilisearch_core::Error::SchemaMissing)?;
 
         match (params.into_inner().primary_key, schema.primary_key()) {
-            (Some(_), Some(_)) => return Err(meilisearch_schema::Error::PrimaryKeyAlreadyPresent.into()),
             (Some(key), None) => document_addition.set_primary_key(key),
             (None, None) => {
                 let key = body
@@ -184,7 +183,7 @@ async fn update_multiple_documents(
                     .ok_or(meilisearch_core::Error::MissingPrimaryKey)?;
                 document_addition.set_primary_key(key);
             }
-            (None, Some(_)) => ()
+            _ => ()
         }
 
         for document in body.into_inner() {
diff --git a/meilisearch-http/tests/settings.rs b/meilisearch-http/tests/settings.rs
index 6b125c13a..98973b56f 100644
--- a/meilisearch-http/tests/settings.rs
+++ b/meilisearch-http/tests/settings.rs
@@ -171,6 +171,8 @@ async fn write_all_and_update() {
         "synonyms": {
             "road": ["street", "avenue"],
             "street": ["avenue"],
+            "HP": ["Harry Potter"],
+            "Harry Potter": ["HP"]
         },
         "attributesForFaceting": ["title"],
     });
@@ -208,6 +210,8 @@ async fn write_all_and_update() {
         "synonyms": {
             "road": ["street", "avenue"],
             "street": ["avenue"],
+            "hp": ["harry potter"],
+            "harry potter": ["hp"]
         },
         "attributesForFaceting": ["title"],
     });