diff --git a/compose/utils.py b/compose/utils.py
index b9b6ab9bd..72e6ced17 100644
--- a/compose/utils.py
+++ b/compose/utils.py
@@ -176,6 +176,7 @@ def unique_everseen(iterable, key=lambda x: x):
     "List unique elements, preserving order. Remember all elements ever seen."
     seen = set()
     for element in iterable:
-        if key(element) not in seen:
-            seen.add(element)
+        unique_key = key(element)
+        if unique_key not in seen:
+            seen.add(unique_key)
             yield element
diff --git a/tests/unit/utils_test.py b/tests/unit/utils_test.py
index 186b6b14e..21b88d962 100644
--- a/tests/unit/utils_test.py
+++ b/tests/unit/utils_test.py
@@ -72,5 +72,7 @@ class TestParseBytes(object):
 
 class TestMoreItertools(object):
     def test_unique_everseen(self):
-        assert list(utils.unique_everseen([2, 1, 2, 1])) == [2, 1]
-        assert list(utils.unique_everseen([2, 1, 2, 1], hash)) == [2, 1]
+        unique = utils.unique_everseen
+        assert list(unique([2, 1, 2, 1])) == [2, 1]
+        assert list(unique([2, 1, 2, 1], hash)) == [2, 1]
+        assert list(unique([2, 1, 2, 1], lambda x: 'key_%s' % x)) == [2, 1]