diff --git a/changelogs/fragments/70784-vault-is-string.yml b/changelogs/fragments/70784-vault-is-string.yml
new file mode 100644
index 00000000000..8dc1164a857
--- /dev/null
+++ b/changelogs/fragments/70784-vault-is-string.yml
@@ -0,0 +1,3 @@
+bugfixes:
+- JSON Encoder - Ensure we treat single vault encrypted values as strings
+  (https://github.com/ansible/ansible/issues/70784)
diff --git a/lib/ansible/module_utils/common/json.py b/lib/ansible/module_utils/common/json.py
index 3018e9e238e..3ac9eecf2b4 100644
--- a/lib/ansible/module_utils/common/json.py
+++ b/lib/ansible/module_utils/common/json.py
@@ -15,15 +15,23 @@ from ansible.module_utils.common._collections_compat import Mapping
 from ansible.module_utils.common.collections import is_sequence
 
 
+def _is_unsafe(value):
+    return getattr(value, '__UNSAFE__', False) and not getattr(value, '__ENCRYPTED__', False)
+
+
+def _is_vault(value):
+    return getattr(value, '__ENCRYPTED__', False)
+
+
 def _preprocess_unsafe_encode(value):
     """Recursively preprocess a data structure converting instances of ``AnsibleUnsafe``
     into their JSON dict representations
 
     Used in ``AnsibleJSONEncoder.iterencode``
     """
-    if getattr(value, '__UNSAFE__', False) and not getattr(value, '__ENCRYPTED__', False):
+    if _is_unsafe(value):
         value = {'__ansible_unsafe': to_text(value, errors='surrogate_or_strict', nonstring='strict')}
-    elif is_sequence(value):
+    elif is_sequence(value) and not _is_vault(value):
         value = [_preprocess_unsafe_encode(v) for v in value]
     elif isinstance(value, Mapping):
         value = dict((k, _preprocess_unsafe_encode(v)) for k, v in value.items())
diff --git a/test/units/parsing/test_ajson.py b/test/units/parsing/test_ajson.py
index 929d19966d8..c38f43ea572 100644
--- a/test/units/parsing/test_ajson.py
+++ b/test/units/parsing/test_ajson.py
@@ -158,6 +158,7 @@ class TestAnsibleJSONEncoder:
         Test for passing AnsibleVaultEncryptedUnicode to AnsibleJSONEncoder.default().
         """
         assert ansible_json_encoder.default(test_input) == {'__ansible_vault': expected}
+        assert json.dumps(test_input, cls=AnsibleJSONEncoder, preprocess_unsafe=True) == '{"__ansible_vault": "%s"}' % expected.replace('\n', '\\n')
 
     @pytest.mark.parametrize(
         'test_input,expected',