diff --git a/meilidb-data/src/database/main_index.rs b/meilidb-data/src/database/main_index.rs
index 9718e3c96..c58b76d47 100644
--- a/meilidb-data/src/database/main_index.rs
+++ b/meilidb-data/src/database/main_index.rs
@@ -7,12 +7,17 @@ use crate::ranked_map::RankedMap;
 
 use super::Error;
 
+const SCHEMA_KEY:     &str = "schema";
+const WORDS_KEY:      &str = "words";
+const SYNONYMS_KEY:   &str = "synonyms";
+const RANKED_MAP_KEY: &str = "ranked-map";
+
 #[derive(Clone)]
 pub struct MainIndex(pub(crate) InnerRawIndex);
 
 impl MainIndex {
     pub fn schema(&self) -> Result<Option<Schema>, Error> {
-        match self.0.get_pinned("schema")? {
+        match self.0.get_pinned(SCHEMA_KEY)? {
             Some(bytes) => {
                 let schema = Schema::read_from_bin(bytes.as_ref())?;
                 Ok(Some(schema))
@@ -24,12 +29,12 @@ impl MainIndex {
     pub fn set_schema(&self, schema: &Schema) -> Result<(), Error> {
         let mut bytes = Vec::new();
         schema.write_to_bin(&mut bytes)?;
-        self.0.set("schema", bytes)?;
+        self.0.set(SCHEMA_KEY, bytes)?;
         Ok(())
     }
 
     pub fn words_set(&self) -> Result<Option<fst::Set>, Error> {
-        match self.0.get_pinned("words")? {
+        match self.0.get_pinned(WORDS_KEY)? {
             Some(bytes) => {
                 let len = bytes.len();
                 let value = Arc::from(bytes.as_ref());
@@ -41,11 +46,11 @@ impl MainIndex {
     }
 
     pub fn set_words_set(&self, value: &fst::Set) -> Result<(), Error> {
-        self.0.set("words", value.as_fst().as_bytes()).map_err(Into::into)
+        self.0.set(WORDS_KEY, value.as_fst().as_bytes()).map_err(Into::into)
     }
 
     pub fn synonyms_set(&self) -> Result<Option<fst::Set>, Error> {
-        match self.0.get_pinned("synonyms")? {
+        match self.0.get_pinned(SYNONYMS_KEY)? {
             Some(bytes) => {
                 let len = bytes.len();
                 let value = Arc::from(bytes.as_ref());
@@ -57,11 +62,11 @@ impl MainIndex {
     }
 
     pub fn set_synonyms_set(&self, value: &fst::Set) -> Result<(), Error> {
-        self.0.set("synonyms", value.as_fst().as_bytes()).map_err(Into::into)
+        self.0.set(SYNONYMS_KEY, value.as_fst().as_bytes()).map_err(Into::into)
     }
 
     pub fn ranked_map(&self) -> Result<Option<RankedMap>, Error> {
-        match self.0.get_pinned("ranked-map")? {
+        match self.0.get_pinned(RANKED_MAP_KEY)? {
             Some(bytes) => {
                 let ranked_map = RankedMap::read_from_bin(bytes.as_ref())?;
                 Ok(Some(ranked_map))
@@ -73,7 +78,7 @@ impl MainIndex {
     pub fn set_ranked_map(&self, value: &RankedMap) -> Result<(), Error> {
         let mut bytes = Vec::new();
         value.write_to_bin(&mut bytes)?;
-        self.0.set("ranked-map", bytes)?;
+        self.0.set(RANKED_MAP_KEY, bytes)?;
         Ok(())
     }
 }