diff --git a/CppHeaderParser/CppHeaderParser.py b/CppHeaderParser/CppHeaderParser.py
index a369308..70cffda 100644
--- a/CppHeaderParser/CppHeaderParser.py
+++ b/CppHeaderParser/CppHeaderParser.py
@@ -3709,11 +3709,28 @@ def toJSON(self, indent=4, separators=None):
         import json
 
         self._strip_parent_keys()
+
+        def clean_dict(markers, keys=[]):
+            if id(markers) in keys:
+                return None
+            elif isinstance(markers, dict):
+                keys_ = keys + [id(markers)]
+                return {
+                    key: clean_dict(markers[key], keys_)
+                    for key, value in markers.items()
+                }
+            elif type(markers) in [list, set, tuple]:
+                return type(markers)(clean_dict(m, keys) for m in markers)
+            return markers
+
         try:
             del self.__dict__["classes_order"]
         except:
             pass
-        return json.dumps(self.__dict__, indent=indent, separators=separators)
+
+        d = self.__dict__
+        d["classes"] = clean_dict(d["classes"])
+        return json.dumps(d, indent=indent, separators=separators, default="")
 
     def __repr__(self):
         rtn = {