diff --git a/packages/mermaid/src/diagram-api/types.ts b/packages/mermaid/src/diagram-api/types.ts
index 7656acb6c..1687e1791 100644
--- a/packages/mermaid/src/diagram-api/types.ts
+++ b/packages/mermaid/src/diagram-api/types.ts
@@ -27,7 +27,7 @@ export interface DiagramDefinition {
   db: DiagramDb;
   renderer: any;
   parser: any;
-  styles: any;
+  styles?: any;
   init?: (config: MermaidConfig) => void;
   injectUtils?: (
     _log: InjectUtils['_log'],