diff --git a/.changeset/gold-shoes-camp.md b/.changeset/gold-shoes-camp.md
new file mode 100644
index 000000000..3018e7381
--- /dev/null
+++ b/.changeset/gold-shoes-camp.md
@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Remove incorrect `style="undefined;"` attributes in some Mermaid diagrams
diff --git a/packages/mermaid/src/rendering-util/rendering-elements/edges.js b/packages/mermaid/src/rendering-util/rendering-elements/edges.js
index 434c53856..ce4244ff2 100644
--- a/packages/mermaid/src/rendering-util/rendering-elements/edges.js
+++ b/packages/mermaid/src/rendering-util/rendering-elements/edges.js
@@ -562,7 +562,7 @@ export const insertEdge = function (elem, edge, clusterDb, diagramType, startNod
   }
   let svgPath;
   let linePath = lineFunction(lineData);
-  const edgeStyles = Array.isArray(edge.style) ? edge.style : [edge.style];
+  const edgeStyles = Array.isArray(edge.style) ? edge.style : edge.style ? [edge.style] : [];
   let strokeColor = edgeStyles.find((style) => style?.startsWith('stroke:'));
 
   if (edge.look === 'handDrawn') {