diff --git a/crates/ra_hir_expand/src/db.rs b/crates/ra_hir_expand/src/db.rs
index 8b92d4c1f8..dc4944c051 100644
--- a/crates/ra_hir_expand/src/db.rs
+++ b/crates/ra_hir_expand/src/db.rs
@@ -1,3 +1,5 @@
+//! Defines database & queries for macro expansion.
+
 use std::sync::Arc;
 
 use mbe::MacroRules;