diff --git a/packages/mermaid/src/diagrams/class/classTypes.ts b/packages/mermaid/src/diagrams/class/classTypes.ts
index 2835ce08a..5eaf4fba8 100644
--- a/packages/mermaid/src/diagrams/class/classTypes.ts
+++ b/packages/mermaid/src/diagrams/class/classTypes.ts
@@ -19,13 +19,13 @@ export interface ClassNode {
 export class ClassMember {
   id!: string;
   cssStyle!: string;
-  memberType!: string;
+  memberType!: 'method' | 'attribute';
   visibility!: string;
   classifier!: string;
   parameters!: string;
   returnType!: string;
 
-  constructor(input: string, memberType: string) {
+  constructor(input: string, memberType: 'method' | 'attribute') {
     this.memberType = memberType;
     this.visibility = '';
     this.classifier = '';