diff --git a/apps/web/components/editors/tiptap/tiptap-mermaid-extension.ts b/apps/web/components/editors/tiptap/tiptap-mermaid-extension.ts
index ba7c77c9b8..092c530b85 100644
--- a/apps/web/components/editors/tiptap/tiptap-mermaid-extension.ts
+++ b/apps/web/components/editors/tiptap/tiptap-mermaid-extension.ts
@@ -14,6 +14,7 @@ import {
   MIN_SCALE,
   MAX_SCALE,
   getSvgDimensions,
+  sanitizeMermaidCode,
 } from "@/components/shared/mermaid-utils";
 
 /**
@@ -239,8 +240,9 @@ class MermaidNodeView implements NodeView {
     if (!mermaidInitialized) initMermaid();
     if (!code.trim()) return;
     const id = `mermaid-${++mermaidIdCounter}`;
+    const sanitizedCode = sanitizeMermaidCode(code);
     mermaid
-      .render(id, code)
+      .render(id, sanitizedCode)
       .then(({ svg }) => {
         this.svgContainer.innerHTML = svg;
         this.updateSizeWrapper();
diff --git a/apps/web/components/shared/mermaid-block.tsx b/apps/web/components/shared/mermaid-block.tsx
index e85c3d9cc5..0c70f803fe 100644
--- a/apps/web/components/shared/mermaid-block.tsx
+++ b/apps/web/components/shared/mermaid-block.tsx
@@ -3,7 +3,14 @@
 import { useEffect, useRef, useState, useCallback } from "react";
 import { useTheme } from "next-themes";
 import { IconZoomIn, IconZoomOut, IconCode } from "@tabler/icons-react";
-import { DEFAULT_SCALE, SCALE_STEP, MIN_SCALE, MAX_SCALE, getSvgDimensions } from "./mermaid-utils";
+import {
+  DEFAULT_SCALE,
+  SCALE_STEP,
+  MIN_SCALE,
+  MAX_SCALE,
+  getSvgDimensions,
+  sanitizeMermaidCode,
+} from "./mermaid-utils";
 
 type MermaidAPI = typeof import("mermaid").default;
 
@@ -36,10 +43,12 @@ export function MermaidBlock({ code }: MermaidBlockProps) {
     const theme = resolvedTheme === "dark" ? "dark" : "default";
     const id = `mermaid-md-${++mermaidIdCounter}`;
 
+    const sanitizedCode = sanitizeMermaidCode(code);
+
     getMermaid()
       .then((mermaid) => {
         mermaid.initialize({ startOnLoad: false, theme, securityLevel: "loose" });
-        return mermaid.render(id, code);
+        return mermaid.render(id, sanitizedCode);
       })
       .then(({ svg }) => {
         if (!cancelled && containerRef.current) {
diff --git a/apps/web/components/shared/mermaid-utils.ts b/apps/web/components/shared/mermaid-utils.ts
index 14dd084841..b00c205d6b 100644
--- a/apps/web/components/shared/mermaid-utils.ts
+++ b/apps/web/components/shared/mermaid-utils.ts
@@ -21,3 +21,51 @@ export function getSvgDimensions(container: HTMLElement): { w: number; h: number
   if (w > 0 && h > 0) return { w, h };
   return null;
 }
+
+/**
+ * Characters that require quoting in mermaid node/edge labels.
+ * Includes: $, #, &, /, and other special chars that cause lexical errors.
+ */
+const SPECIAL_CHARS_RE = /[$#&/\\<>{}]/;
+
+/**
+ * Preprocesses mermaid code to quote text containing special characters.
+ * Mermaid requires quotes around text with special chars like $, /, etc.
+ *
+ * Handles:
+ * - Node labels: A[text] -> A["text"] if text contains special chars
+ * - Edge labels: -->|text| -> -->|"text"| if text contains special chars
+ * - Subgraph titles: subgraph text -> subgraph "text" if text contains special chars
+ */
+export function sanitizeMermaidCode(code: string): string {
+  // Quote node labels: [text] or (text) or {text} or ([text]) or [[text]] etc.
+  // Match brackets that aren't already quoted
+  let result = code.replace(/(\[+)([^\]"]+?)(\]+)/g, (match, open, text, close) => {
+    if (SPECIAL_CHARS_RE.test(text) && !text.startsWith('"')) {
+      return `${open}"${text}"${close}`;
+    }
+    return match;
+  });
+
+  // Quote edge labels: |text|
+  result = result.replace(/\|([^|"]+?)\|/g, (match, text) => {
+    if (SPECIAL_CHARS_RE.test(text) && !text.startsWith('"')) {
+      return `|"${text}"|`;
+    }
+    return match;
+  });
+
+  // Quote parentheses labels: (text) for stadium/circle nodes
+  result = result.replace(/(\(+)([^)"]+?)(\)+)/g, (match, open, text, close) => {
+    // Skip if it looks like a subgraph or keyword
+    if (/^(subgraph|end|graph|flowchart|sequenceDiagram)\b/.test(text.trim())) {
+      return match;
+    }
+    if (SPECIAL_CHARS_RE.test(text) && !text.startsWith('"')) {
+      return `${open}"${text}"${close}`;
+    }
+    return match;
+  });
+
+  return result;
+}