diff --git a/packages/mermaid/src/diagrams/flowchart/flowDb.ts b/packages/mermaid/src/diagrams/flowchart/flowDb.ts
index a41466b09..2329f0ace 100644
--- a/packages/mermaid/src/diagrams/flowchart/flowDb.ts
+++ b/packages/mermaid/src/diagrams/flowchart/flowDb.ts
@@ -85,7 +85,7 @@ export class FlowDB implements DiagramDB {
     return common.sanitizeText(txt, this.config);
   }
 
-  private sanitizeNodeLabelType(labelType: string) {
+  private sanitizeNodeLabelType(labelType?: string) {
     switch (labelType) {
       case 'markdown':
       case 'string':
@@ -219,7 +219,7 @@ export class FlowDB implements DiagramDB {
 
       if (doc?.label) {
         vertex.text = doc?.label;
-        vertex.labelType = this.sanitizeNodeLabelType(doc?.labelType ?? 'markdown');
+        vertex.labelType = this.sanitizeNodeLabelType(doc?.labelType);
       }
       if (doc?.icon) {
         vertex.icon = doc?.icon;
@@ -279,7 +279,7 @@ export class FlowDB implements DiagramDB {
       if (edge.text.startsWith('"') && edge.text.endsWith('"')) {
         edge.text = edge.text.substring(1, edge.text.length - 1);
       }
-      edge.labelType = linkTextObj.type;
+      edge.labelType = this.sanitizeNodeLabelType(linkTextObj.type);
     }
 
     if (type !== undefined) {
@@ -714,7 +714,7 @@ You have to call mermaid.initialize.`
       title: title.trim(),
       classes: [],
       dir,
-      labelType: _title.type,
+      labelType: this.sanitizeNodeLabelType(_title?.type),
     };
 
     log.info('Adding', subGraph.id, subGraph.nodes, subGraph.dir);