diff --git a/crates/typst/src/lib.rs b/crates/typst/src/lib.rs
index aad474a1b..e17d93468 100644
--- a/crates/typst/src/lib.rs
+++ b/crates/typst/src/lib.rs
@@ -191,7 +191,7 @@ fn deduplicate(mut diags: EcoVec<SourceDiagnostic>) -> EcoVec<SourceDiagnostic>
 /// [edit](Source::edit) them in-place to benefit from better incremental
 /// performance.
 #[comemo::track]
-pub trait World {
+pub trait World: Send + Sync {
     /// The standard library.
     ///
     /// Can be created through `Library::build()`.