diff --git a/package.json b/package.json
index 0a64b2d4..ddaee4b8 100644
--- a/package.json
+++ b/package.json
@@ -26,6 +26,7 @@
     "build-example": "npm install --no-save --ignore-scripts grunt grunt-cli gulp through2",
     "example": "cd example && node standalone.js && grunt markdownlint --force && gulp markdownlint",
     "clone-test-repos": "make-dir test-repos && cd test-repos && git clone https://github.com/eslint/eslint eslint-eslint --depth 1 --no-tags --quiet && git clone https://github.com/mkdocs/mkdocs mkdocs-mkdocs --depth 1 --no-tags --quiet && git clone https://github.com/pi-hole/docs pi-hole-docs --depth 1 --no-tags --quiet",
+    "clone-test-repos-large": "npm run clone-test-repos && cd test-repos && git clone https://github.com/dotnet/docs dotnet-docs --depth 1 --no-tags --quiet",
     "lint-test-repos": "node test/markdownlint-test-repos.js",
     "clean-test-repos": "rimraf test-repos"
   },
diff --git a/test/markdownlint-test-repos.js b/test/markdownlint-test-repos.js
index 50d3bbb9..2149a40f 100644
--- a/test/markdownlint-test-repos.js
+++ b/test/markdownlint-test-repos.js
@@ -2,6 +2,7 @@
 
 "use strict";
 
+const { existsSync } = require("fs");
 const { join } = require("path");
 const { promisify } = require("util");
 const globby = require("globby");
@@ -91,3 +92,18 @@ tape("https://github.com/pi-hole/docs", (test) => {
   const configPath = join(rootDir, ".markdownlint.json");
   lintTestRepo(test, globPatterns, configPath);
 });
+
+// Optional repositories (very large)
+
+const dotnetDocsDir = "./test-repos/dotnet-docs";
+if (existsSync(dotnetDocsDir)) {
+  tape("https://github.com/dotnet/docs", (test) => {
+    const rootDir = dotnetDocsDir;
+    const globPatterns = [
+      join(rootDir, "**/*.md"),
+      "!" + join(rootDir, "samples/**/*.md")
+    ];
+    const configPath = join(rootDir, ".markdownlint.json");
+    lintTestRepo(test, globPatterns, configPath);
+  });
+}