diff --git a/CHANGELOG.md b/CHANGELOG.md
index a75fb98fb..50394ee44 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 # Unreleased
 
+- Fix resolver when toplevel requirements are also in pinned
+  subdependency (#450)
+
 # 0.180.6
 
 - Exclude irrelevant pip constraints (#417)
diff --git a/pip_requ/resolver.py b/pip_requ/resolver.py
index b64cc4144..4196dd308 100644
--- a/pip_requ/resolver.py
+++ b/pip_requ/resolver.py
@@ -3,6 +3,7 @@
                         unicode_literals)
 
 import os
+import copy
 from functools import partial
 from itertools import chain, count
 
@@ -157,7 +158,8 @@ def _group_constraints(self, constraints):
                 continue
 
             ireqs = iter(ireqs)
-            combined_ireq = next(ireqs)
+            # deepcopy the accumulator so as to not modify the self.our_constraints invariant
+            combined_ireq = copy.deepcopy(next(ireqs))
             combined_ireq.comes_from = None
             for ireq in ireqs:
                 # NOTE we may be losing some info on dropped reqs here
diff --git a/tests/conftest.py b/tests/conftest.py
index a0d4f1047..9ca7da94b 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -10,6 +10,7 @@
 from pip_requ.repositories.base import BaseRepository
 from pip_requ.resolver import Resolver
 from pip_requ.utils import as_tuple, key_from_req, make_install_requirement
+from pip_requ.exceptions import NoCandidateFound
 
 
 class FakeRepository(BaseRepository):
@@ -31,7 +32,10 @@ def find_best_match(self, ireq, prereleases=False):
         if ireq.editable:
             return ireq
 
-        versions = ireq.specifier.filter(self.index[key_from_req(ireq.req)], prereleases=prereleases)
+        versions = list(ireq.specifier.filter(self.index[key_from_req(ireq.req)],
+                                              prereleases=prereleases))
+        if not versions:
+            raise NoCandidateFound(ireq, self.index[key_from_req(ireq.req)])
         best_version = max(versions, key=Version)
         return make_install_requirement(key_from_req(ireq.req), best_version, ireq.extras, constraint=ireq.constraint)
 
diff --git a/tests/fixtures/fake-index.json b/tests/fixtures/fake-index.json
index c04e574e9..f316688c9 100644
--- a/tests/fixtures/fake-index.json
+++ b/tests/fixtures/fake-index.json
@@ -4,20 +4,32 @@
   },
   "amqp": {
     "1.4.9": {"": []},
-    "2.0.2": {"": ["vine>=1.1.1"]}
+    "2.0.2": {"": ["vine>=1.1.1"]},
+    "2.1.4": {"": ["vine>=1.1.3"]}
   },
   "arrow": {
     "0.5.0": {"": ["python-dateutil"]},
     "0.5.4": {"": ["python-dateutil"]}
   },
   "billiard": {
-    "3.3.0.23": {"": []}
+    "3.3.0.23": {"": []},
+    "3.5.0.2": {"": []}
   },
   "celery": {
+    "3.1.18": {"": [
+      "kombu<3.1,>=3.0.25",
+      "pytz>dev",
+      "billiard<3.4,>=3.3.0.20"
+    ]},
     "3.1.23": {"": [
-      "kombu>=3.0.34",
+      "kombu>=3.0.34,<4",
       "pytz>dev",
       "billiard>=3.3.0.23"
+    ]},
+    "4.0.2": {"": [
+      "kombu<5.0,>=4.0.2",
+      "pytz>dev",
+      "billiard<3.6.0,>=3.5.0.2"
     ]}
   },
   "click": {
@@ -29,6 +41,11 @@
     "1.7.7": {"": []},
     "1.8": {"": []}
   },
+  "fake-piptools-test-with-pinned-deps": {
+    "0.1": {"": [
+        "celery==3.1.18"
+    ]}
+  },
   "flask": {
     "0.10.1": {"": [
       "Jinja2>=2.4",
@@ -76,6 +93,9 @@
     "3.0.35": {"": [
       "anyjson>=0.3.3",
       "amqp>=1.4.9,<2.0"
+    ]},
+    "4.0.2": {"": [
+      "amqp<3.0,>=2.1.4"
     ]}
   },
   "librabbitmq": {
@@ -113,7 +133,8 @@
     "3.2.2": {"": []}
   },
   "vine": {
-    "1.1.1": {"": []}
+    "1.1.1": {"": []},
+    "1.1.3": {"": []}
   },
   "werkzeug": {
     "0.6": {"": []},
diff --git a/tests/test_resolver.py b/tests/test_resolver.py
index 9b8c850c9..c48f28503 100644
--- a/tests/test_resolver.py
+++ b/tests/test_resolver.py
@@ -69,15 +69,31 @@
 
         # We must remove child dependencies from result if parent is removed (e.g. vine from amqp>=2.0)
         # See: GH-370
-        (['celery', 'librabbitmq'],
+        # because of upated dependencies in the test index, we need to pin celery
+        # in order to reproduce vine removal (because it was readded in later releases)
+        (['celery<=3.1.23', 'librabbitmq'],
          [
-             'amqp==1.4.9',
-             'anyjson==0.3.3',
-             'billiard==3.3.0.23',
-             'celery==3.1.23',
-             'kombu==3.0.35',
-             'librabbitmq==1.6.1',
-             'pytz==2016.4']
+            'amqp==1.4.9',
+            'anyjson==0.3.3',
+            'billiard==3.5.0.2',
+            'celery==3.1.23',
+            'kombu==3.0.35',
+            'librabbitmq==1.6.1',
+            'pytz==2016.4']
+         ),
+
+        # Support specifying loose top-level requirements that could also appear as
+        # pinned subdependencies.
+        (['billiard', 'celery',
+          'fake-piptools-test-with-pinned-deps'],
+         [
+            'amqp==1.4.9',
+            'anyjson==0.3.3',
+            'billiard==3.3.0.23',
+            'celery==3.1.18',  # this is pinned from test subdependency
+            'fake-piptools-test-with-pinned-deps==0.1',
+            'kombu==3.0.35',
+            'pytz==2016.4']
          ),
 
         # We shouldn't include irrelevant pip constraints