diff --git a/packages/mermaid/src/rendering-util/icons.ts b/packages/mermaid/src/rendering-util/icons.ts
index 76a03cde5..199bc4206 100644
--- a/packages/mermaid/src/rendering-util/icons.ts
+++ b/packages/mermaid/src/rendering-util/icons.ts
@@ -1,8 +1,14 @@
 import { log } from '$root/logger.js';
-import type { IconifyJSON } from '@iconify/types';
+import type { ExtendedIconifyIcon, IconifyIcon, IconifyJSON } from '@iconify/types';
 import type { IconifyIconCustomisations } from '@iconify/utils';
 import { getIconData, iconToHTML, iconToSVG, replaceIDs, stringToIcon } from '@iconify/utils';
 
+export const unknownIcon: IconifyIcon = {
+  body: '<g><rect width="80" height="80" style="fill: #087ebf; stroke-width: 0px;"/><text transform="translate(21.16 64.67)" style="fill: #fff; font-family: ArialMT, Arial; font-size: 67.75px;"><tspan x="0" y="0">?</tspan></text></g>',
+  height: 80,
+  width: 80,
+};
+
 export const iconsStore = new Map<string, IconifyJSON>();
 
 export const registerIconPacks = (...iconPacks: IconifyJSON[]) => {
@@ -11,26 +17,47 @@ export const registerIconPacks = (...iconPacks: IconifyJSON[]) => {
   }
 };
 
-export const getIconSVG = (iconName: string, customisations?: IconifyIconCustomisations) => {
+const getRegisteredIconData = (iconName: string, fallbackPrefix?: string) => {
+  const data = stringToIcon(iconName, true, fallbackPrefix !== undefined);
+  if (!data) {
+    throw new Error(`Invalid icon name: ${iconName}`);
+  }
+  const prefix = data.prefix || fallbackPrefix;
+  if (!prefix) {
+    throw new Error(`Icon name must contain a prefix: ${iconName}`);
+  }
+  const icons = iconsStore.get(prefix);
+  if (!icons) {
+    throw new Error(`Icon set not found: ${data.prefix}`);
+  }
+  const iconData = getIconData(icons, data.name);
+  if (!iconData) {
+    throw new Error(`Icon not found: ${iconName}`);
+  }
+  return iconData;
+};
+
+export const isIconAvailable = (iconName: string) => {
   try {
-    const data = stringToIcon(iconName, true, true);
-    if (!data) {
-      throw new Error(`Invalid icon name: ${iconName}`);
-    }
-    const icons = iconsStore.get(data.prefix || 'default');
-    if (!icons) {
-      throw new Error(`Icon set not found: ${data.prefix}`);
-    }
-    const iconData = getIconData(icons, data.name);
-    if (!iconData) {
-      throw new Error(`Icon not found: ${iconName}`);
-    }
-    const renderData = iconToSVG(iconData, customisations);
-    const svg = iconToHTML(replaceIDs(renderData.body), renderData.attributes);
-    return svg;
-  } catch (e) {
-    log.error(e);
-    // Return unknown icon svg.
-    return '<g><rect width="80" height="80" style="fill: #087ebf; stroke-width: 0px;"/><text transform="translate(21.16 64.67)" style="fill: #fff; font-family: ArialMT, Arial; font-size: 67.75px;"><tspan x="0" y="0">?</tspan></text></g>';
+    getRegisteredIconData(iconName);
+    return true;
+  } catch {
+    return false;
   }
 };
+
+export const getIconSVG = (
+  iconName: string,
+  customisations?: IconifyIconCustomisations & { fallbackPrefix?: string }
+) => {
+  let iconData: ExtendedIconifyIcon;
+  try {
+    iconData = getRegisteredIconData(iconName, customisations?.fallbackPrefix);
+  } catch (e) {
+    log.error(e);
+    iconData = unknownIcon;
+  }
+  const renderData = iconToSVG(iconData, customisations);
+  const svg = iconToHTML(replaceIDs(renderData.body), renderData.attributes);
+  return svg;
+};