diff --git a/src/serialize/per_type/dict.rs b/src/serialize/per_type/dict.rs
index 89f7ca00..4790b9b9 100644
--- a/src/serialize/per_type/dict.rs
+++ b/src/serialize/per_type/dict.rs
@@ -346,14 +346,24 @@ impl DictNonStrKey {
                     Ok(CompactString::from(uni.unwrap()))
                 }
             }
+            ObType::Unknown => {
+                let key_str_obj = ffi!(PyObject_Str(key));
+                debug_assert!(ffi!(Py_REFCNT(key_str_obj)) >= 2);
+                if unlikely!(key_str_obj.is_null()) {
+                    Err(SerializeError::DictKeyInvalidType)
+                } else {
+                    let ret = Self::pyobject_to_string(key_str_obj, opts);
+                    ffi!(Py_DECREF(key_str_obj));
+                    ret
+                }
+            }
             ObType::Tuple
             | ObType::NumpyScalar
             | ObType::NumpyArray
             | ObType::Dict
             | ObType::List
             | ObType::Dataclass
-            | ObType::Fragment
-            | ObType::Unknown => Err(SerializeError::DictKeyInvalidType),
+            | ObType::Fragment => Err(SerializeError::DictKeyInvalidType),
         }
     }
 }
diff --git a/test/test_non_str_keys.py b/test/test_non_str_keys.py
index fad13486..7cdec4b1 100644
--- a/test/test_non_str_keys.py
+++ b/test/test_non_str_keys.py
@@ -244,13 +244,6 @@ def test_dict_keys_str(self):
             orjson.dumps({"1": True}, option=orjson.OPT_NON_STR_KEYS) == b'{"1":true}'
         )
 
-    def test_dict_keys_type(self):
-        class Obj:
-            a: str
-
-        val = Obj()
-        with pytest.raises(orjson.JSONEncodeError):
-            orjson.dumps({val: True}, option=orjson.OPT_NON_STR_KEYS)
 
     @pytest.mark.skipif(numpy is None, reason="numpy is not installed")
     def test_dict_keys_array(self):
@@ -290,11 +283,8 @@ def test_dict_keys_tuple(self):
         with pytest.raises(orjson.JSONEncodeError):
             orjson.dumps(obj, option=orjson.OPT_NON_STR_KEYS)
 
-    def test_dict_keys_unknown(self):
-        with pytest.raises(orjson.JSONEncodeError):
-            orjson.dumps({frozenset(): True}, option=orjson.OPT_NON_STR_KEYS)
 
-    def test_dict_keys_no_str_call(self):
+    def test_dict_keys_str_call(self):
         class Obj:
             a: str
 
@@ -302,5 +292,7 @@ def __str__(self):
                 return "Obj"
 
         val = Obj()
-        with pytest.raises(orjson.JSONEncodeError):
-            orjson.dumps({val: True}, option=orjson.OPT_NON_STR_KEYS)
+        assert (
+            orjson.dumps({val: True}, option=orjson.OPT_NON_STR_KEYS) == b'{"Obj":true}'
+        )
+