diff --git a/py/obj.c b/py/obj.c
index afbc62a65fcee..a825efc3c5a8f 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -144,6 +144,13 @@ void mp_obj_print_helper(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t
     }
     #endif
     const mp_obj_type_t *type = mp_obj_get_type(o_in);
+    // CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
+    #if MICROPY_PY_JSON
+    if (kind == PRINT_JSON && !(type->flags & MP_TYPE_FLAG_PRINT_JSON)) {
+        mp_raise_msg_varg(&mp_type_TypeError,
+            MP_ERROR_TEXT("can't convert %q to %q"), type->name, MP_QSTR_json);
+    }
+    #endif
     if (MP_OBJ_TYPE_HAS_SLOT(type, print)) {
         MP_OBJ_TYPE_GET_SLOT(type, print)((mp_print_t *)print, o_in, kind);
     } else {
diff --git a/py/obj.h b/py/obj.h
index 70fdeeebde4d6..255a00b314f5e 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -581,6 +581,8 @@ typedef mp_obj_t (*mp_fun_kw_t)(size_t n, const mp_obj_t *, mp_map_t *);
 #define MP_TYPE_FLAG_ITER_IS_CUSTOM (0x0100)
 #define MP_TYPE_FLAG_ITER_IS_STREAM (MP_TYPE_FLAG_ITER_IS_ITERNEXT | MP_TYPE_FLAG_ITER_IS_CUSTOM)
 #define MP_TYPE_FLAG_INSTANCE_TYPE (0x0200)
+// CIRCUITPY-CHANGE: check for valid types in json dumps
+#define MP_TYPE_FLAG_PRINT_JSON (0x0400)
 
 typedef enum {
     PRINT_STR = 0,
diff --git a/py/objbool.c b/py/objbool.c
index 5b3e3660e9510..990f52bb26fe4 100644
--- a/py/objbool.c
+++ b/py/objbool.c
@@ -84,11 +84,12 @@ static mp_obj_t bool_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_
     return mp_binary_op(op, MP_OBJ_NEW_SMALL_INT(value), rhs_in);
 }
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     // can match all numeric types
     mp_type_bool,
     MP_QSTR_bool,
-    MP_TYPE_FLAG_EQ_CHECKS_OTHER_TYPE,
+    MP_TYPE_FLAG_EQ_CHECKS_OTHER_TYPE | MP_TYPE_FLAG_PRINT_JSON,
     make_new, bool_make_new,
     print, bool_print,
     unary_op, bool_unary_op,
diff --git a/py/objdict.c b/py/objdict.c
index 96a659d36e048..7094a1c1f99f2 100644
--- a/py/objdict.c
+++ b/py/objdict.c
@@ -710,10 +710,11 @@ static const mp_rom_map_elem_t dict_locals_dict_table[] = {
 
 static MP_DEFINE_CONST_DICT(dict_locals_dict, dict_locals_dict_table);
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_dict,
     MP_QSTR_dict,
-    MP_TYPE_FLAG_ITER_IS_GETITER,
+    MP_TYPE_FLAG_ITER_IS_GETITER | MP_TYPE_FLAG_PRINT_JSON,
     make_new, mp_obj_dict_make_new,
     print, dict_print,
     unary_op, dict_unary_op,
@@ -724,10 +725,11 @@ MP_DEFINE_CONST_OBJ_TYPE(
     );
 
 #if MICROPY_PY_COLLECTIONS_ORDEREDDICT
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_ordereddict,
     MP_QSTR_OrderedDict,
-    MP_TYPE_FLAG_ITER_IS_GETITER,
+    MP_TYPE_FLAG_ITER_IS_GETITER | MP_TYPE_FLAG_PRINT_JSON,
     make_new, mp_obj_dict_make_new,
     print, dict_print,
     unary_op, dict_unary_op,
diff --git a/py/objfloat.c b/py/objfloat.c
index b3a1f692594ad..6f248cdadfc9e 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -186,8 +186,9 @@ static mp_obj_t float_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs
     return mp_obj_float_binary_op(op, lhs_val, rhs_in);
 }
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
-    mp_type_float, MP_QSTR_float, MP_TYPE_FLAG_EQ_NOT_REFLEXIVE | MP_TYPE_FLAG_EQ_CHECKS_OTHER_TYPE,
+    mp_type_float, MP_QSTR_float, MP_TYPE_FLAG_EQ_NOT_REFLEXIVE | MP_TYPE_FLAG_EQ_CHECKS_OTHER_TYPE | MP_TYPE_FLAG_PRINT_JSON,
     make_new, float_make_new,
     print, float_print,
     unary_op, float_unary_op,
diff --git a/py/objint.c b/py/objint.c
index 197625ced815c..7895f4f201ed3 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -588,10 +588,11 @@ static const mp_rom_map_elem_t int_locals_dict_table[] = {
 
 static MP_DEFINE_CONST_DICT(int_locals_dict, int_locals_dict_table);
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_int,
     MP_QSTR_int,
-    MP_TYPE_FLAG_NONE,
+    MP_TYPE_FLAG_PRINT_JSON,
     make_new, mp_obj_int_make_new,
     print, mp_obj_int_print,
     unary_op, mp_obj_int_unary_op,
diff --git a/py/objlist.c b/py/objlist.c
index 475002239ca76..2c1545d877715 100644
--- a/py/objlist.c
+++ b/py/objlist.c
@@ -485,10 +485,11 @@ static const mp_rom_map_elem_t list_locals_dict_table[] = {
 
 static MP_DEFINE_CONST_DICT(list_locals_dict, list_locals_dict_table);
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_list,
     MP_QSTR_list,
-    MP_TYPE_FLAG_ITER_IS_GETITER,
+    MP_TYPE_FLAG_ITER_IS_GETITER | MP_TYPE_FLAG_PRINT_JSON,
     make_new, mp_obj_list_make_new,
     print, list_print,
     unary_op, list_unary_op,
diff --git a/py/objnone.c b/py/objnone.c
index a8ce8ebfedf82..1e2016abd9fb7 100644
--- a/py/objnone.c
+++ b/py/objnone.c
@@ -43,10 +43,11 @@ static void none_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_
     }
 }
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_NoneType,
     MP_QSTR_NoneType,
-    MP_TYPE_FLAG_NONE,
+    MP_TYPE_FLAG_PRINT_JSON,
     print, none_print
     );
 
diff --git a/py/objstr.c b/py/objstr.c
index 0b2517197a0bd..342affb514dd4 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -2203,10 +2203,11 @@ MP_DEFINE_CONST_DICT_WITH_SIZE(mp_obj_memoryview_locals_dict,
 #if !MICROPY_PY_BUILTINS_STR_UNICODE
 static mp_obj_t mp_obj_new_str_iterator(mp_obj_t str, mp_obj_iter_buf_t *iter_buf);
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_str,
     MP_QSTR_str,
-    MP_TYPE_FLAG_NONE,
+    MP_TYPE_FLAG_PRINT_JSON,
     make_new, mp_obj_str_make_new,
     print, str_print,
     binary_op, mp_obj_str_binary_op,
diff --git a/py/objstrunicode.c b/py/objstrunicode.c
index 203d3858e60da..a158b91236588 100644
--- a/py/objstrunicode.c
+++ b/py/objstrunicode.c
@@ -236,10 +236,11 @@ static mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     }
 }
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_str,
     MP_QSTR_str,
-    MP_TYPE_FLAG_ITER_IS_GETITER,
+    MP_TYPE_FLAG_ITER_IS_GETITER | MP_TYPE_FLAG_PRINT_JSON,
     make_new, mp_obj_str_make_new,
     print, uni_print,
     unary_op, uni_unary_op,
diff --git a/py/objtuple.c b/py/objtuple.c
index afa80799af58e..ec1545abb84ea 100644
--- a/py/objtuple.c
+++ b/py/objtuple.c
@@ -232,10 +232,11 @@ static const mp_rom_map_elem_t tuple_locals_dict_table[] = {
 
 static MP_DEFINE_CONST_DICT(tuple_locals_dict, tuple_locals_dict_table);
 
+// CIRCUITPY-CHANGE: Diagnose json.dump on invalid types
 MP_DEFINE_CONST_OBJ_TYPE(
     mp_type_tuple,
     MP_QSTR_tuple,
-    MP_TYPE_FLAG_ITER_IS_GETITER,
+    MP_TYPE_FLAG_ITER_IS_GETITER | MP_TYPE_FLAG_PRINT_JSON,
     make_new, mp_obj_tuple_make_new,
     print, mp_obj_tuple_print,
     unary_op, mp_obj_tuple_unary_op,
diff --git a/tests/extmod/json_dumps_extra.py b/tests/extmod/json_dumps_extra.py
index 9074416a99d93..a410b0ee0ef63 100644
--- a/tests/extmod/json_dumps_extra.py
+++ b/tests/extmod/json_dumps_extra.py
@@ -1,9 +1,6 @@
 # test uPy json behaviour that's not valid in CPy
-
-try:
-    import json
-except ImportError:
-    print("SKIP")
-    raise SystemExit
+# CIRCUITPY-CHANGE: This behavior matches CPython
+print("SKIP")
+raise SystemExit
 
 print(json.dumps(b"1234"))