diff --git a/lib/md045.js b/lib/md045.js
index 3590c9826..7f875fc9b 100644
--- a/lib/md045.js
+++ b/lib/md045.js
@@ -32,8 +32,8 @@ module.exports = {
     const html = filterByTypes(params.parsers.micromark.tokens, [ "htmlText" ]);
     for (const token of html) {
       const htmlTagInfo = getHtmlTagInfo(token);
-      if (htmlTagInfo && htmlTagInfo.name === "img") {
-        const hasAltAttribute = new RegExp(/alt=/);
+      if (htmlTagInfo && htmlTagInfo.name.toLowerCase() === "img") {
+        const hasAltAttribute = new RegExp(/alt=/i);
         if (!hasAltAttribute.test(token.text)) {
           const range = [
             token.startColumn,