diff --git a/index.js b/index.js
index 1dd37fa..fae4424 100644
--- a/index.js
+++ b/index.js
@@ -1,25 +1,79 @@
-const CONDITIONAL_COMMENT_REGEX = /(<!(--)?\[if\s[()\w\s|&!]+\]>(?:<!--+>)?)((?:.|\n)*?)((?:<!--)?<!\[endif\]\2>)/gi;
+// Token regexes to support nested conditional comments
+const OPEN_REGEX = /<!(--)?\[if\s[()\w\s|&!]+\]>(?:<!--+>)?/gi;
+// Capture whether the close carries trailing dashes ("--") before '>' to enforce symmetry
+const CLOSE_REGEX = /(?:<!--)?<!\[endif\](--)?>/gi;
 
 module.exports = function findConditionalComments(str) {
-  let comments = [];
-
-  let result;
-  while ((result = CONDITIONAL_COMMENT_REGEX.exec(str)) !== null) {
-    const [match, open, commentDashes, content, close] = result;
-
-    const bubble = open.endsWith("-->");
-
-    comments.push({
-      isComment: open.startsWith("<!--"),
-      open,
-      close,
-      bubble,
-      downlevel: bubble || commentDashes !== "--" ? "revealed" : "hidden",
-      range: [
-        CONDITIONAL_COMMENT_REGEX.lastIndex - match.length,
-        CONDITIONAL_COMMENT_REGEX.lastIndex,
-      ],
-    });
+  const comments = [];
+
+  // Use a stack to handle nested conditional comments
+  const stack = [];
+  let position = 0;
+
+  while (position < str.length) {
+    // Find next open and next close from current position
+    OPEN_REGEX.lastIndex = position;
+    CLOSE_REGEX.lastIndex = position;
+
+    const openMatch = OPEN_REGEX.exec(str);
+    const closeMatch = CLOSE_REGEX.exec(str);
+
+    // If neither token is found, we're done
+    if (!openMatch && !closeMatch) {
+      break;
+    }
+
+    // Choose the earliest token occurrence
+    const nextOpenIndex = openMatch ? openMatch.index : Infinity;
+    const nextCloseIndex = closeMatch ? closeMatch.index : Infinity;
+
+    if (nextOpenIndex < nextCloseIndex) {
+      // Process opening token
+      const openText = openMatch[0];
+      const openStart = openMatch.index;
+      const openEnd = OPEN_REGEX.lastIndex;
+
+      const isComment = openText.startsWith("<!--");
+      const bubble = openText.endsWith("-->");
+
+      stack.push({
+        open: openText,
+        start: openStart,
+        end: openEnd,
+        isComment,
+        bubble,
+      });
+
+      position = openEnd;
+      continue;
+    }
+
+    // Process closing token
+    const closeText = closeMatch[0];
+    const closeStart = closeMatch.index;
+    const closeEnd = CLOSE_REGEX.lastIndex;
+
+    if (stack.length > 0) {
+      const openState = stack[stack.length - 1];
+      const closeHasDashes = Boolean(closeMatch[1]);
+      const openRequiresDashes = openState.isComment; // HTML comment style requires '-->'
+
+      if (closeHasDashes === openRequiresDashes) {
+        // Valid matching close for the most recent open
+        stack.pop();
+        comments.push({
+          isComment: openState.isComment,
+          open: openState.open,
+          close: closeText,
+          bubble: openState.bubble,
+          downlevel:
+            openState.bubble || !openState.isComment ? "revealed" : "hidden",
+          range: [openState.start, closeEnd],
+        });
+      }
+    }
+
+    position = closeEnd;
   }
 
   return comments;
diff --git a/index.test.js b/index.test.js
index 17621c7..ced1318 100644
--- a/index.test.js
+++ b/index.test.js
@@ -68,3 +68,54 @@ test("correctly marks comments as downlevel-revealed or downlevel-hidden", () =>
     `)[0].downlevel
   ).toEqual("revealed");
 });
+
+test("supports nested conditional comments", () => {
+  const html = `
+    <!--[if mso]>
+      Outer start
+      <!--[if gte mso 15]>Inner<![endif]-->
+      Outer end
+    <![endif]-->
+  `;
+
+  const result = findConditionalComments(html);
+
+  expect(result.length).toBe(2);
+
+  // Identify outer and inner by range size
+  const sorted = [...result].sort(
+    (a, b) => a.range[1] - a.range[0] - (b.range[1] - b.range[0])
+  );
+  const inner = sorted[0];
+  const outer = sorted[1];
+
+  expect(inner.open.startsWith("<!--[if gte mso 15]>")).toBe(true);
+  expect(inner.close).toMatch(/<!\[endif\]-->/);
+  expect(inner.isComment).toBe(true);
+  expect(inner.downlevel).toBe("hidden");
+
+  expect(outer.open.startsWith("<!--[if mso]>")).toBe(true);
+  expect(outer.close).toMatch(/<!\[endif\]-->/);
+  expect(outer.isComment).toBe(true);
+  expect(outer.downlevel).toBe("hidden");
+
+  // Inner range should be fully inside outer range
+  expect(inner.range[0]).toBeGreaterThan(outer.range[0]);
+  expect(inner.range[1]).toBeLessThan(outer.range[1]);
+});
+
+test("rejects mismatched closing dashes for HTML-comment style open", () => {
+  const html = `
+    <!--[if mso]>Bad<![endif]>
+  `;
+  const result = findConditionalComments(html);
+  expect(result.length).toBe(0);
+});
+
+test("rejects mismatched closing dashes for downlevel-revealed open (non-comment)", () => {
+  const html = `
+    <![if mso]>Bad<![endif]-->
+  `;
+  const result = findConditionalComments(html);
+  expect(result.length).toBe(0);
+});
diff --git a/package-lock.json b/package-lock.json
index 6d46078..314e3b2 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "find-conditional-comments",
-  "version": "0.0.4",
+  "version": "0.0.6",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "find-conditional-comments",
-      "version": "0.0.4",
+      "version": "0.0.6",
       "license": "MIT",
       "devDependencies": {
         "husky": "^4.3.0",