diff --git a/milli/src/error.rs b/milli/src/error.rs
new file mode 100644
index 000000000..02740377c
--- /dev/null
+++ b/milli/src/error.rs
@@ -0,0 +1,42 @@
+use std::io;
+
+use crate::{DocumentId, FieldId};
+
+pub enum Error {
+    InternalError(InternalError),
+    IoError(io::Error),
+    UserError(UserError),
+}
+
+pub enum InternalError {
+    DatabaseMissingEntry(DatabaseMissingEntry),
+    FieldIdMapMissingEntry(FieldIdMapMissingEntry),
+    IndexingMergingKeys(IndexingMergingKeys),
+}
+
+pub enum IndexingMergingKeys {
+    DocIdWordPosition,
+    Document,
+    MainFstDeserialization,
+    WordLevelPositionDocids,
+    WordPrefixLevelPositionDocids,
+}
+
+pub enum FieldIdMapMissingEntry {
+    DisplayedFieldId { field_id: FieldId },
+    DisplayedFieldName { field_name: String },
+    FacetedFieldName { field_name: String },
+    FilterableFieldName { field_name: String },
+    SearchableFieldName { field_name: String },
+}
+
+pub enum DatabaseMissingEntry {
+    DocumentId { internal_id: DocumentId },
+    FacetValuesDocids,
+    IndexCreationTime,
+    IndexUpdateTime,
+}
+
+pub enum UserError {
+
+}
diff --git a/milli/src/lib.rs b/milli/src/lib.rs
index 8c1ed514c..b7401330a 100644
--- a/milli/src/lib.rs
+++ b/milli/src/lib.rs
@@ -1,6 +1,7 @@
 #[macro_use] extern crate pest_derive;
 
 mod criterion;
+mod error;
 mod external_documents_ids;
 mod fields_ids_map;
 mod search;