diff --git a/mistral/tests/unit/engine/test_yaql_functions.py b/mistral/tests/unit/engine/test_yaql_functions.py
index 76e1d419e..c3a6c6828 100644
--- a/mistral/tests/unit/engine/test_yaql_functions.py
+++ b/mistral/tests/unit/engine/test_yaql_functions.py
@@ -13,7 +13,6 @@
 #    limitations under the License.
 
 from oslo_config import cfg
-import six
 
 from mistral.db.v2 import api as db_api
 from mistral.services import workflows as wf_service
@@ -432,42 +431,3 @@ class YAQLFunctionsEngineTest(engine_test_base.EngineTestCase):
         self.assertIsNotNone(json_str)
         self.assertIn('"key1": "foo"', json_str)
         self.assertIn('"key2": "bar"', json_str)
-
-    def test_built_in_str_function(self):
-        wf_text = """---
-        version: '2.0'
-
-        wf:
-          input:
-            - my_list
-
-          tasks:
-            task1:
-              publish:
-                val: <% str($.my_list) %>
-        """
-
-        wf_service.create_workflows(wf_text)
-
-        wf_ex = self.engine.start_workflow(
-            'wf',
-            wf_input={
-                'my_list': [
-                    {
-                        'k1': 'v1',
-                        'k2': 'v2'
-                    }
-                ]
-            }
-        )
-
-        self.await_workflow_success(wf_ex.id)
-
-        with db_api.transaction(read_only=True):
-            wf_ex = db_api.get_workflow_execution(wf_ex.id)
-
-            val = wf_ex.task_executions[0].published['val']
-
-            self.assertIsInstance(val, six.string_types)
-            self.assertIn('[', val)
-            self.assertIn(']', val)
diff --git a/mistral/utils/expression_utils.py b/mistral/utils/expression_utils.py
index 2e4f4035e..1155b10f0 100644
--- a/mistral/utils/expression_utils.py
+++ b/mistral/utils/expression_utils.py
@@ -14,7 +14,6 @@
 #    limitations under the License.
 
 from functools import partial
-import six
 import warnings
 
 from oslo_log import log as logging
@@ -40,27 +39,6 @@ LOG = logging.getLogger(__name__)
 ROOT_YAQL_CONTEXT = None
 
 
-def _convert_yaql_input_data(obj, rec=None):
-    # NOTE(rakhmerov): We have to define our own wrapper function
-    # around the function 'convert_input_data' from 'yaql_utils'
-    # because the latter always converts all sequences (except strings)
-    # into tuples, and it in turn breaks a number of things. For example,
-    # if we use the built-in 'str' YAQL function with an argument of the
-    # type 'list' then the result will be '(item1, item2 ..., itemN,)'
-    # instead of '[item1, item2 ..., itemN]'.
-    # So we override this behavior for sequences that are not strings and
-    # tuples.
-    if rec is None:
-        rec = _convert_yaql_input_data
-
-    if (isinstance(obj, yaql_utils.SequenceType) and
-            not isinstance(obj, six.string_types) and
-            not isinstance(obj, tuple)):
-        return list(rec(t, rec) for t in obj)
-    else:
-        return yaql_utils.convert_input_data(obj, rec)
-
-
 def get_yaql_context(data_context):
     global ROOT_YAQL_CONTEXT
 
@@ -70,7 +48,7 @@ def get_yaql_context(data_context):
         _register_yaql_functions(ROOT_YAQL_CONTEXT)
 
     new_ctx = ROOT_YAQL_CONTEXT.create_child_context()
-    new_ctx['$'] = _convert_yaql_input_data(data_context)
+    new_ctx['$'] = yaql_utils.convert_input_data(data_context)
 
     if isinstance(data_context, dict):
         new_ctx['__env'] = data_context.get('__env')