diff --git a/heat/engine/hot/functions.py b/heat/engine/hot/functions.py
index 33b75f4e4d..a309392b31 100644
--- a/heat/engine/hot/functions.py
+++ b/heat/engine/hot/functions.py
@@ -1643,12 +1643,14 @@ class ListConcat(function.Function):
         for m in args:
             ret_list.extend(ensure_list(m))
 
-        if self._unique:
-            for i in ret_list:
-                while ret_list.count(i) > 1:
-                    del ret_list[ret_list.index(i)]
+        if not self._unique:
+            return ret_list
 
-        return ret_list
+        unique_list = []
+        for item in ret_list:
+            if item not in unique_list:
+                unique_list.append(item)
+        return unique_list
 
 
 class ListConcatUnique(ListConcat):
diff --git a/heat/tests/test_hot.py b/heat/tests/test_hot.py
index a0ec62ae82..a4f4c3d32a 100644
--- a/heat/tests/test_hot.py
+++ b/heat/tests/test_hot.py
@@ -2399,7 +2399,7 @@ resources:
         self.assertEqual(snippet_resolved, resolved)
 
     def test_list_concat_unique(self):
-        snippet = {'list_concat_unique': [['v1', 'v2'], ['v2', 'v3']]}
+        snippet = {'list_concat_unique': [['v1', 'v2'], ['v1', 'v3']]}
         snippet_resolved = ['v1', 'v2', 'v3']
         tmpl = template.Template(hot_pike_tpl_empty)
         resolved = self.resolve(snippet, tmpl)