diff --git a/packages/docusaurus-migrate/src/index.ts b/packages/docusaurus-migrate/src/index.ts
index 880454e5c1..c29991ac32 100644
--- a/packages/docusaurus-migrate/src/index.ts
+++ b/packages/docusaurus-migrate/src/index.ts
@@ -513,11 +513,13 @@ function migrateVersionedDocs(
   });
   const files = walk(path.join(newDir, 'versioned_docs'));
   files.forEach((pathToFile) => {
-    const content = fs.readFileSync(pathToFile).toString();
-    fs.writeFileSync(
-      pathToFile,
-      sanitizedFileContent(content.replace(versionRegex, ''), migrateMDFiles),
-    );
+    if (path.extname(pathToFile) === '.md') {
+      const content = fs.readFileSync(pathToFile).toString();
+      fs.writeFileSync(
+        pathToFile,
+        sanitizedFileContent(content.replace(versionRegex, ''), migrateMDFiles),
+      );
+    }
   });
 }
 
@@ -696,8 +698,10 @@ function migrateLatestDocs(
     );
     const files = walk(path.join(siteDir, '..', 'docs'));
     files.forEach((file) => {
-      const content = String(fs.readFileSync(file));
-      fs.writeFileSync(file, sanitizedFileContent(content, migrateMDFiles));
+      if (path.extname(file) === '.md') {
+        const content = fs.readFileSync(file).toString();
+        fs.writeFileSync(file, sanitizedFileContent(content, migrateMDFiles));
+      }
     });
     logger.success('Migrated docs to version 2');
   } else {
@@ -749,11 +753,11 @@ export async function migrateMDToMDX(
   fs.mkdirpSync(newDir);
   fs.copySync(siteDir, newDir);
   const files = walk(newDir);
-  files.forEach((file) => {
-    fs.writeFileSync(
-      file,
-      sanitizedFileContent(String(fs.readFileSync(file)), true),
-    );
+  files.forEach((filePath) => {
+    if (path.extname(filePath) === '.md') {
+      const content = fs.readFileSync(filePath).toString();
+      fs.writeFileSync(filePath, sanitizedFileContent(content, true));
+    }
   });
   logger.success`Successfully migrated path=${siteDir} to path=${newDir}`;
 }