diff --git a/spacy/tests/doc/test_json_doc_conversion.py b/spacy/tests/doc/test_json_doc_conversion.py
index 19698cfb2..11a1817e6 100644
--- a/spacy/tests/doc/test_json_doc_conversion.py
+++ b/spacy/tests/doc/test_json_doc_conversion.py
@@ -370,3 +370,12 @@ def test_json_to_doc_validation_error(doc):
     doc_json.pop("tokens")
     with pytest.raises(ValueError):
         Doc(doc.vocab).from_json(doc_json, validate=True)
+
+
+def test_to_json_underscore_doc_getters(doc):
+    def get_text_length(doc):
+        return len(doc.text)
+
+    Doc.set_extension("text_length", getter=get_text_length)
+    doc_json = doc.to_json(underscore=["text_length"])
+    assert doc_json["_"]["text_length"] == get_text_length(doc)
diff --git a/spacy/tokens/doc.pyx b/spacy/tokens/doc.pyx
index 295f91c28..f2621292c 100644
--- a/spacy/tokens/doc.pyx
+++ b/spacy/tokens/doc.pyx
@@ -1668,6 +1668,20 @@ cdef class Doc:
 
         if underscore:
             user_keys = set()
+            # Handle doc attributes with .get to include values from getters
+            # and not only values stored in user_data, for backwards
+            # compatibility
+            for attr in underscore:
+                if self.has_extension(attr):
+                    if "_" not in data:
+                        data["_"] = {}
+                    value = self._.get(attr)
+                    if not srsly.is_json_serializable(value):
+                        raise ValueError(Errors.E107.format(attr=attr, value=repr(value)))
+                    data["_"][attr] = value
+                    user_keys.add(attr)
+            # Token and span attributes only include values stored in user_data
+            # and not values generated by getters
             if self.user_data:
                 for data_key, value in self.user_data.copy().items():
                     if type(data_key) == tuple and len(data_key) >= 4 and data_key[0] == "._.":
@@ -1678,20 +1692,15 @@ cdef class Doc:
                             user_keys.add(attr)
                             if not srsly.is_json_serializable(value):
                                 raise ValueError(Errors.E107.format(attr=attr, value=repr(value)))
-                            # Check if doc attribute
-                            if start is None:
-                                if "_" not in data:
-                                    data["_"] = {}
-                                data["_"][attr] = value
-                            # Check if token attribute
-                            elif end is None:
+                            # Token attribute
+                            if start is not None and end is None:
                                 if "underscore_token" not in data:
                                     data["underscore_token"] = {}
                                 if attr not in data["underscore_token"]:
                                     data["underscore_token"][attr] = []
                                 data["underscore_token"][attr].append({"start": start, "value": value})
-                            # Else span attribute
-                            else:
+                            # Span attribute
+                            elif start is not None and end is not None:
                                 if "underscore_span" not in data:
                                     data["underscore_span"] = {}
                                 if attr not in data["underscore_span"]: