diff --git a/muppet/format.py b/muppet/format.py
index 3cc09968314fa907eff821d3a9075cd9f0b70813..9e5be76f3f7f4b8c85463fb69f7e3c12d6076346 100644
--- a/muppet/format.py
+++ b/muppet/format.py
@@ -150,7 +150,6 @@ def format_class(d_type: DefinedType | PuppetClass) -> Tuple[str, str]:
     name, body = format_docstring(d_type.name, d_type.docstring)
     out += body
 
-    out += '<pre class="highlight-muppet"><code class="puppet">'
     # ------ Old ---------------------------------------
     # t = parse_puppet(d_type.source)
     # data = parse(t, 0, ['root'])
@@ -158,11 +157,24 @@ def format_class(d_type: DefinedType | PuppetClass) -> Tuple[str, str]:
     # out += render(renderer, data)
     # ------ New ---------------------------------------
     try:
-        out += parse_puppet(d_type.source, d_type.name)
+        result = parse_puppet(d_type.source, d_type.name)
+        out += '<pre class="highlight-muppet"><code class="puppet">'
+        out += result
+        out += '</code></pre>'
     except ParseError as e:
         logger.error("Parsing %(name)s failed: %(err)s",
                      {'name': d_type.name, 'err': e})
-    out += '</code></pre>'
+        out += f'<div class="error">{e}</div>'
+        out += '<pre><code class="puppet">'
+        if e.pos:
+            out += d_type.source[:e.pos]
+            out += '<span class="error">'
+            out += d_type.source[e.pos]
+            out += '</span>'
+            out += d_type.source[e.pos+1:]
+        else:
+            out += d_type.source
+        out += '</code></pre>'
     return name, out
 
 
diff --git a/static-src/style.scss b/static-src/style.scss
index 57c4387f3a8d2c2df6f01ac7a2bd47587290247b..ec677d7a7b34fa866f95f2a7d9151eb3bbadb599 100644
--- a/static-src/style.scss
+++ b/static-src/style.scss
@@ -183,6 +183,21 @@ ul.toc {
 
 /* -------------------------------------------------- */
 
+div.error {
+	white-space: pre;
+	background: pink;
+	border: 2px solid red;
+	border-radius: 1pt;
+	font-family: mono;
+}
+
+span.error {
+	background: red;
+	color: white;
+}
+
+/* -------------------------------------------------- */
+
 @import "colorscheme_default";
 
 .highlight-pygments {