diff --git a/src/runtime/internal/style_manager.ts b/src/runtime/internal/style_manager.ts
index 8fc6514cbc..25dfa53169 100644
--- a/src/runtime/internal/style_manager.ts
+++ b/src/runtime/internal/style_manager.ts
@@ -3,8 +3,8 @@ import { raf } from './environment';
 
 type DocStyles = [CSSStyleSheet, Record<string, true>];
 
-let active_docs = new Set<Document>();
-let doc_styles = new Map<Document, DocStyles>();
+const active_docs = new Set<Document>();
+const doc_styles = new Map<Document, DocStyles>();
 let active = 0;
 
 // https://github.com/darkskyapp/string-hash/blob/master/index.js