diff --git a/packages/streamdown/lib/mermaid/utils.ts b/packages/streamdown/lib/mermaid/utils.ts
index 0242d786..8a0fe818 100644
--- a/packages/streamdown/lib/mermaid/utils.ts
+++ b/packages/streamdown/lib/mermaid/utils.ts
@@ -1,3 +1,13 @@
+/**
+ * Ensure SVG string has required XML namespaces for canvas rendering
+ */
+function normalizeSvg(svg: string): string {
+  if (svg.includes("xlink:href") && !svg.includes("xmlns:xlink")) {
+    return svg.replace("<svg", '<svg xmlns:xlink="http://www.w3.org/1999/xlink"');
+  }
+  return svg;
+}
+
 /**
  * Convert SVG string to PNG blob for export
  */
@@ -8,9 +18,11 @@ export const svgToPngBlob = (
   const scale = options?.scale ?? 5;
 
   return new Promise((resolve, reject) => {
+    const normalized = normalizeSvg(svgString);
+
     const encoded =
       "data:image/svg+xml;base64," +
-      btoa(unescape(encodeURIComponent(svgString)));
+      btoa(unescape(encodeURIComponent(normalized)));
 
     const img = new Image();
     img.crossOrigin = "anonymous";