diff --git a/src/calibre/gui2/tweak_book/editor/syntax/html.c b/src/calibre/gui2/tweak_book/editor/syntax/html.c
index 00402aa14e..9367763b7b 100644
--- a/src/calibre/gui2/tweak_book/editor/syntax/html.c
+++ b/src/calibre/gui2/tweak_book/editor/syntax/html.c
@@ -68,6 +68,7 @@ html_Tag_copy(html_Tag *self, PyObject *args, PyObject *kwargs) {
 
 static PyObject *
 html_Tag_compare(html_Tag *a, html_Tag *b, int op) {
+    if (!PyObject_TypeCheck(a, &html_TagType) || !PyObject_TypeCheck(b, &html_TagType)) Py_RETURN_FALSE;
     switch (op) {
         case Py_EQ:
             if (COMPARE(name, Py_EQ) && COMPARE(lang, Py_EQ)) Py_RETURN_TRUE;
@@ -277,6 +278,7 @@ end:
 
 static PyObject *
 html_State_compare(html_State *a, html_State *b, int op) {
+    if (!PyObject_TypeCheck(a, &html_StateType) || !PyObject_TypeCheck(b, &html_StateType)) Py_RETURN_FALSE;
     switch (op) {
         case Py_EQ:
             if (COMPARE(parse, Py_EQ) && COMPARE(sub_parser_state, Py_EQ) && COMPARE(tag_being_defined, Py_EQ) && COMPARE(attribute_name, Py_EQ) && COMPARE(tags, Py_EQ)) Py_RETURN_TRUE;
diff --git a/src/calibre/gui2/tweak_book/editor/syntax/html.py b/src/calibre/gui2/tweak_book/editor/syntax/html.py
index 72682ce770..a1a03d23f8 100644
--- a/src/calibre/gui2/tweak_book/editor/syntax/html.py
+++ b/src/calibre/gui2/tweak_book/editor/syntax/html.py
@@ -86,7 +86,10 @@ else:
             self.lang = lang
 
         def __eq__(self, other):
-            return self.name == other.name and self.lang == other.lang
+            try:
+                return self.name == other.name and self.lang == other.lang
+            except AttributeError:
+                return False
 
         def copy(self):
             ans = Tag(self.name, self.bold, self.italic, self.lang)
@@ -117,13 +120,16 @@ else:
             return ans
 
         def __eq__(self, other):
-            return (
-                self.parse == other.parse and
-                self.sub_parser_state == other.sub_parser_state and
-                self.tag_being_defined == other.tag_being_defined and
-                self.attribute_name == other.attribute_name and
-                self.tags == other.tags
-            )
+            try:
+                return (
+                    self.parse == other.parse and
+                    self.sub_parser_state == other.sub_parser_state and
+                    self.tag_being_defined == other.tag_being_defined and
+                    self.attribute_name == other.attribute_name and
+                    self.tags == other.tags
+                )
+            except AttributeError:
+                return False
 
         def __ne__(self, other):
             return not self.__eq__(other)