diff --git a/himl/interpolation.py b/himl/interpolation.py
index 2a7b9793..97692760 100644
--- a/himl/interpolation.py
+++ b/himl/interpolation.py
@@ -143,10 +143,7 @@ def loop_all_items(self, data, process_func):
         if isinstance(data, list):
             items = []
             for item in data:
-                if isinstance(item, list):
-                    items.extend(item)
-                else:
-                    items.append(self.loop_all_items(item, process_func))
+                items.append(self.loop_all_items(item, process_func))
             return items
         if isinstance(data, dict):
             for key in data:
diff --git a/tests/test_interpolation.py b/tests/test_interpolation.py
new file mode 100644
index 00000000..2a48e68e
--- /dev/null
+++ b/tests/test_interpolation.py
@@ -0,0 +1,37 @@
+# Copyright 2019 Adobe. All rights reserved.
+# This file is licensed to you under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License. You may obtain a copy
+# of the License at http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software distributed under
+# the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
+# OF ANY KIND, either express or implied. See the License for the specific language
+# governing permissions and limitations under the License.
+
+from pytest import mark
+from himl.interpolation import DictIterator
+
+
+@mark.parametrize(
+    "start, end, func",
+    [
+        (
+            {"test": [1, 3, 2], "another": {"thing": "is", "some": "data"}},
+            {"test": [1, 3, 2], "another": {"thing": "is", "some": "data"}},
+            lambda x: x,
+        ),
+        (
+            {"test": [1, 3, 2], "another": {"thing": "is", "some": "data"}},
+            {"test": [1, 3, 2], "another": {"thing": "isis", "some": "datadata"}},
+            lambda x: 2 * x,
+        ),
+        (
+            [["a", "set"], ["of", "test"], ["data", "for", "testing"], [1, 2, 3]],
+            [["a_", "set_"], ["of_", "test_"], ["data_", "for_", "testing_"], [1, 2, 3]],
+            lambda x: x + "_",
+        ),
+    ],
+)
+def test_dict_iterator(start, end, func):
+    looper = DictIterator()
+    assert looper.loop_all_items(start, func) == end