diff --git a/components/FileViewer.tsx b/components/FileViewer.tsx
index 40ee2ec74..a99a1813f 100644
--- a/components/FileViewer.tsx
+++ b/components/FileViewer.tsx
@@ -1,6 +1,6 @@
 "use client";
 
-import { useEffect, useState, useRef, useCallback, type CSSProperties, type MouseEvent } from "react";
+import { useEffect, useState, useRef, useCallback, useMemo, type CSSProperties, type MouseEvent } from "react";
 import {
   Prism as SyntaxHighlighter,
   createElement as renderSyntaxNode,
@@ -19,7 +19,7 @@ import {
 } from "@/lib/file-types";
 import { encodeFilePathForApi, getFileDirectory, getFileName, getRelativeFilePath } from "@/lib/file-paths";
 import { resolveLocalFileHref } from "@/lib/file-links";
-import { markdownPreviewRehypePlugins, markdownPreviewRemarkPlugins } from "@/lib/markdown";
+import { markdownPreviewRehypePlugins, markdownPreviewRemarkPlugins, normalizeDisplayMath } from "@/lib/markdown";
 import { CodeBlock, MermaidBlock } from "./MermaidBlock";
 import { parseUnifiedPatch } from "@/lib/patch";
 import type { GitFileDiffResponse } from "@/lib/git-types";
@@ -895,6 +895,11 @@ function TextFileViewer({ filePath, cwd, sourceSessionId, onOpenFile, onMentionL
     if (!hasGitDiff && displayMode === "diff") setDisplayMode("source");
   }, [displayMode, hasGitDiff]);
 
+  const markdownPreview = useMemo(
+    () => (data?.language === "markdown" ? normalizeDisplayMath(data.content) : ""),
+    [data],
+  );
+
   useEffect(() => {
     const updateSelectedLineRange = () => {
       const root = contentRef.current;
@@ -1146,7 +1151,7 @@ function TextFileViewer({ filePath, cwd, sourceSessionId, onOpenFile, onMentionL
                 },
               }}
             >
-              {data.content}
+              {markdownPreview}
             </ReactMarkdown>
           </div>
         ) : (
diff --git a/components/MarkdownBody.tsx b/components/MarkdownBody.tsx
index 01bb4f251..0a4a8a47a 100644
--- a/components/MarkdownBody.tsx
+++ b/components/MarkdownBody.tsx
@@ -4,7 +4,7 @@ import { useMemo, type MouseEvent } from "react";
 import ReactMarkdown from "react-markdown";
 import { resolveLocalFileHref } from "@/lib/file-links";
 import { encodeFilePathForApi } from "@/lib/file-paths";
-import { markdownRehypePlugins, markdownRemarkPlugins } from "@/lib/markdown";
+import { markdownRehypePlugins, markdownRemarkPlugins, normalizeDisplayMath } from "@/lib/markdown";
 import { MermaidBlock, CodeBlock } from "./MermaidBlock";
 
 interface MarkdownBodyProps {
@@ -98,32 +98,3 @@ export function MarkdownBody({ children, className, isStreaming, cwd, onOpenFile
     </div>
   );
 }
-
-function normalizeDisplayMath(markdown: string): string {
-  const lineBreak = markdown.includes("\r\n") ? "\r\n" : "\n";
-  const lines = markdown.split(/\r?\n/);
-  let fence: { marker: string; size: number } | null = null;
-
-  return lines
-    .map((line) => {
-      const fenceMatch = line.match(/^ {0,3}(`{3,}|~{3,})/);
-      if (fenceMatch) {
-        const marker = fenceMatch[1][0];
-        const size = fenceMatch[1].length;
-        if (!fence) fence = { marker, size };
-        else if (marker === fence.marker && size >= fence.size) fence = null;
-        return line;
-      }
-
-      if (fence) return line;
-
-      const displayMathMatch = line.match(/^([ \t]{0,3})\$\$(.+)\$\$[ \t]*$/);
-      if (!displayMathMatch) return line;
-
-      const math = displayMathMatch[2].trim();
-      if (!math) return line;
-
-      return `${displayMathMatch[1]}$$${lineBreak}${math}${lineBreak}${displayMathMatch[1]}$$`;
-    })
-    .join(lineBreak);
-}
diff --git a/lib/markdown.ts b/lib/markdown.ts
index 9ccd5940b..f85af1e26 100644
--- a/lib/markdown.ts
+++ b/lib/markdown.ts
@@ -14,8 +14,37 @@ const markdownSanitizeSchema = {
   strip: [...(defaultSchema.strip || []), "iframe", "object", "style", "form"],
 };
 
+export function normalizeDisplayMath(markdown: string): string {
+  const lineBreak = markdown.includes("\r\n") ? "\r\n" : "\n";
+  const lines = markdown.split(/\r?\n/);
+  let fence: { marker: string; size: number } | null = null;
+
+  return lines
+    .map((line) => {
+      const fenceMatch = line.match(/^ {0,3}(`{3,}|~{3,})/);
+      if (fenceMatch) {
+        const marker = fenceMatch[1][0];
+        const size = fenceMatch[1].length;
+        if (!fence) fence = { marker, size };
+        else if (marker === fence.marker && size >= fence.size) fence = null;
+        return line;
+      }
+
+      if (fence) return line;
+
+      const displayMathMatch = line.match(/^([ \t]{0,3})\$\$(.+)\$\$[ \t]*$/);
+      if (!displayMathMatch) return line;
+
+      const math = displayMathMatch[2].trim();
+      if (!math) return line;
+
+      return `${displayMathMatch[1]}$$${lineBreak}${math}${lineBreak}${displayMathMatch[1]}$$`;
+    })
+    .join(lineBreak);
+}
+
 export const markdownRemarkPlugins: ReactMarkdownOptions["remarkPlugins"] = [remarkGfm, remarkMath];
-export const markdownPreviewRemarkPlugins: ReactMarkdownOptions["remarkPlugins"] = [remarkGfm];
+export const markdownPreviewRemarkPlugins: ReactMarkdownOptions["remarkPlugins"] = [remarkGfm, remarkMath];
 
 export const markdownRehypePlugins: ReactMarkdownOptions["rehypePlugins"] = [
   rehypeRaw,
@@ -26,4 +55,5 @@ export const markdownRehypePlugins: ReactMarkdownOptions["rehypePlugins"] = [
 export const markdownPreviewRehypePlugins: ReactMarkdownOptions["rehypePlugins"] = [
   rehypeRaw,
   [rehypeSanitize, markdownSanitizeSchema],
+  [rehypeKatex, { throwOnError: false, strict: false }],
 ];