diff --git a/ftplugin/markdown.vim b/ftplugin/markdown.vim
index 60505cd3..fc3fa4d9 100644
--- a/ftplugin/markdown.vim
+++ b/ftplugin/markdown.vim
@@ -1,6 +1,6 @@
 "TODO print messages when on visual mode. I only see VISUAL, not the messages.
 
-" Function interface phylosophy:
+" Function interface philosophy:
 "
 " - functions take arbitrary line numbers as parameters.
 "    Current cursor line is only a suitable default parameter.
@@ -56,7 +56,7 @@ let s:levelRegexpDict = {
     \ 6: '\v^######[^#]@='
 \ }
 
-" Maches any header level of any type.
+" Matches any header level of any type.
 "
 " This could be deduced from `s:levelRegexpDict`, but it is more
 " efficient to have a single regexp for this.
diff --git a/syntax/markdown.vim b/syntax/markdown.vim
index 37494832..fc9f34a6 100644
--- a/syntax/markdown.vim
+++ b/syntax/markdown.vim
@@ -116,6 +116,7 @@ syn region mkdNonListItemBlock start="\(\%^\(\s*\([-*+]\|\d\+\.\)\s\+\)\@!\|\n\(
 syn match  mkdRule         /^\s*\*\s\{0,1}\*\s\{0,1}\*\(\*\|\s\)*$/
 syn match  mkdRule         /^\s*-\s\{0,1}-\s\{0,1}-\(-\|\s\)*$/
 syn match  mkdRule         /^\s*_\s\{0,1}_\s\{0,1}_\(_\|\s\)*$/
+syn keyword mkdTodo TODO FIXME XXX TBD contained containedin=htmlComment,htmlCommentPart
 
 " YAML frontmatter
 if get(g:, 'vim_markdown_frontmatter', 0)
@@ -180,6 +181,7 @@ HtmlHiLink mkdLinkDef          mkdID
 HtmlHiLink mkdLinkDefTarget    mkdURL
 HtmlHiLink mkdLinkTitle        htmlString
 HtmlHiLink mkdDelimiter        Delimiter
+HtmlHiLink mkdTodo             Todo
 
 let b:current_syntax = 'mkd'
 
diff --git a/test/syntax.vader b/test/syntax.vader
index b111de0d..4619617e 100644
--- a/test/syntax.vader
+++ b/test/syntax.vader
@@ -1303,6 +1303,43 @@ Execute (HTML tag in text):
   AssertEqual SyntaxOf('<span>'), 'htmlTag'
   AssertEqual SyntaxOf('</span>'), 'htmlEndTag'
 
+Given markdown;
+<!-- TODO FIXME XXX TBD hello -->
+
+Execute (todo inside HTML comment):
+  AssertEqual SyntaxOf('TODO'), 'mkdTodo'
+  AssertEqual SyntaxOf('FIXME'), 'mkdTodo'
+  AssertEqual SyntaxOf('XXX'), 'mkdTodo'
+  AssertEqual SyntaxOf('TBD'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('hello'), 'mkdTodo'
+
+Given markdown;
+<!-- ATODO BFIXME CXXX DTBD -->
+
+Execute (fake todo inside HTML comment):
+  AssertNotEqual SyntaxOf('TODO'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('FIXME'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('XXX'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('TBD'), 'mkdTodo'
+
+Given markdown;
+TODO FIXME XXX TBD
+
+Execute (todo outside HTML comment):
+  AssertNotEqual SyntaxOf('TODO'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('FIXME'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('XXX'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('TBD'), 'mkdTodo'
+
+Given markdown;
+> TODO FIXME XXX TBD
+
+Execute (todo inside non-HTML comment):
+  AssertNotEqual SyntaxOf('TODO'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('FIXME'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('XXX'), 'mkdTodo'
+  AssertNotEqual SyntaxOf('TBD'), 'mkdTodo'
+
 Given markdown;
 # _h1_