diff --git a/crates/ra_db/src/input.rs b/crates/ra_db/src/input.rs
index a5f4e489f7b..c103503bd55 100644
--- a/crates/ra_db/src/input.rs
+++ b/crates/ra_db/src/input.rs
@@ -31,9 +31,23 @@
 
 #[derive(Default, Clone, Debug, PartialEq, Eq)]
 pub struct SourceRoot {
+    /// Sysroot or crates.io library.
+    ///
+    /// Libraries are considered mostly immutable, this assumption is used to
+    /// optimize salsa's query structure
+    pub is_library: bool,
     pub files: FxHashMap<RelativePathBuf, FileId>,
 }
 
+impl SourceRoot {
+    pub fn new() -> SourceRoot {
+        Default::default()
+    }
+    pub fn new_library() -> SourceRoot {
+        SourceRoot { is_library: true, ..SourceRoot::new() }
+    }
+}
+
 /// `CrateGraph` is a bit of information which turns a set of text files into a
 /// number of Rust crates. Each crate is defined by the `FileId` of its root module,
 /// the set of cfg flags (not yet implemented) and the set of dependencies. Note
diff --git a/crates/ra_ide_api/src/change.rs b/crates/ra_ide_api/src/change.rs
index 895b1e966de..8d9918d164d 100644
--- a/crates/ra_ide_api/src/change.rs
+++ b/crates/ra_ide_api/src/change.rs
@@ -163,7 +163,8 @@ pub(crate) fn apply_change(&mut self, change: AnalysisChange) {
         if !change.new_roots.is_empty() {
             let mut local_roots = Vec::clone(&self.local_roots());
             for (root_id, is_local) in change.new_roots {
-                self.set_source_root(root_id, Default::default());
+                let root = if is_local { SourceRoot::new() } else { SourceRoot::new_library() };
+                self.set_source_root(root_id, Arc::new(root));
                 if is_local {
                     local_roots.push(root_id);
                 }