diff --git a/openstack_requirements/cmds/build_lower_constraints.py b/openstack_requirements/cmds/build_lower_constraints.py
index b79eaa1762..438270f5d7 100644
--- a/openstack_requirements/cmds/build_lower_constraints.py
+++ b/openstack_requirements/cmds/build_lower_constraints.py
@@ -48,7 +48,8 @@ def merge_constraints_sets(constraints_sets):
     all_constraints = collections.defaultdict(list)
     for constraints_set in constraints_sets:
         for constraint_name, constraint in constraints_set.items():
-            all_constraints[constraint_name].extend(constraint)
+            if constraint_name:
+                all_constraints[constraint_name].extend(constraint)
     for constraint_name, constraints in sorted(all_constraints.items()):
         val = max((c[0] for c in constraints), key=get_requirements_version)
         yield val.to_line()
diff --git a/openstack_requirements/tests/test_build_lower_constraints.py b/openstack_requirements/tests/test_build_lower_constraints.py
index 75b2f3ac71..5f820f4885 100644
--- a/openstack_requirements/tests/test_build_lower_constraints.py
+++ b/openstack_requirements/tests/test_build_lower_constraints.py
@@ -55,3 +55,15 @@ class BuildLowerConstraintsTest(testtools.TestCase):
             expected,
             list(build_lower_constraints.merge_constraints_sets(inputs))
         )
+
+    def test_one_input_file_with_comments(self):
+        inputs = [
+            requirement.parse('package==1.2.3\n # package2==0.9.8'),
+        ]
+        expected = [
+            'package==1.2.3\n',
+        ]
+        self.assertEqual(
+            expected,
+            list(build_lower_constraints.merge_constraints_sets(inputs))
+        )