diff --git a/src/calibre/srv/html_as_json.cpp b/src/calibre/srv/html_as_json.cpp
index 3c3a0fff42..d2805b1659 100644
--- a/src/calibre/srv/html_as_json.cpp
+++ b/src/calibre/srv/html_as_json.cpp
@@ -311,7 +311,7 @@ class Serializer {
 		}
 		if (!write_str_literal("{\"n\":")) return false;
 		if (!this->write_string_as_json(tag_name)) return false;
-		if (nsindex > -1) {
+		if (nsindex > 0) {
 			char buf[32];
 			this->write_data(buf, snprintf(buf, sizeof(buf), ",\"s\":%d", nsindex));
 		}
diff --git a/src/calibre/srv/tests/content.py b/src/calibre/srv/tests/content.py
index 8b5dcd4c11..2cc151d77f 100644
--- a/src/calibre/srv/tests/content.py
+++ b/src/calibre/srv/tests/content.py
@@ -252,14 +252,14 @@ class ContentTest(LibraryBaseTest):
             bc = data['tree']['c'][1]['c']
             self.ae(bc, body_children)
 
-        t('<p>a<!--c-->t</p>l', [{"n":"p","s":0,"x":"a","l":"l","c":[{"s":"c","x":"c","l":"t"}]}])
-        t('<p class="foo" id="bar">a', [{"n":"p","s":0,"x":"a","a":[['class','foo'],['id','bar']]}])
+        t('<p>a<!--c-->t</p>l', [{"n":"p","x":"a","l":"l","c":[{"s":"c","x":"c","l":"t"}]}])
+        t('<p class="foo" id="bar">a', [{"n":"p","x":"a","a":[['class','foo'],['id','bar']]}])
         t(
             '<svg xlink:href="h"></svg>', [{'n': 'svg', 's': 1, 'a': [['href', 'h', 2]]}],
             ('http://www.w3.org/1999/xhtml', 'http://www.w3.org/2000/svg', 'http://www.w3.org/1999/xlink')
         )
         text = '🐈\n\t\\mūs"'
-        t("<p id='{}'>Peña".format(text), [{"n":"p","s":0,"x":"Peña","a":[['id',text]]}])
+        t("<p id='{}'>Peña".format(text), [{"n":"p","x":"Peña","a":[['id',text]]}])
         text = 'a' * (127 * 1024)
-        t('<p>{0}<p>{0}'.format(text), [{"n":"p","s":0,"x":text}, {'n':'p','s':0,'x':text}])
+        t('<p>{0}<p>{0}'.format(text), [{"n":"p","x":text}, {'n':'p','x':text}])
     # }}}