diff --git a/src/collections/string_pool.rs b/src/collections/string_pool.rs
index fb897861609d1cef87d11cc845c627fd07d968c8..2b9f7856adfdc27897aa5027b8f5bbb8d55d1255 100644
--- a/src/collections/string_pool.rs
+++ b/src/collections/string_pool.rs
@@ -152,6 +152,13 @@ impl Drop for StringPool {
     }
 }
 
+// String pool cannot be cloned, and the created `StringRef` instances remain
+// allocated until the end of the program, so it is always safe to send. It is
+// also sync in the sense that it becomes an immutable thing after compilation,
+// but lets not derive that if we would ever become a multithreaded compiler in
+// the future.
+unsafe impl Send for StringPool {}
+
 #[cfg(test)]
 mod tests {
     use super::*;