diff --git a/piptools/repositories/base.py b/piptools/repositories/base.py
index 6ac06bad9..0343fe7d7 100644
--- a/piptools/repositories/base.py
+++ b/piptools/repositories/base.py
@@ -45,6 +45,7 @@ def allow_all_wheels(self):
         Monkey patches pip.Wheel to allow wheels from all platforms and Python versions.
         """
 
+    @abstractmethod
     def copy_ireq_dependencies(self, source, dest):
         """
         Notifies the repository that `dest` is a copy of `source`, and so it
diff --git a/piptools/repositories/local.py b/piptools/repositories/local.py
index ec3a7963b..b2356d811 100644
--- a/piptools/repositories/local.py
+++ b/piptools/repositories/local.py
@@ -92,3 +92,6 @@ def get_hashes(self, ireq):
     def allow_all_wheels(self):
         with self.repository.allow_all_wheels():
             yield
+
+    def copy_ireq_dependencies(self, source, dest):
+        self.repository.copy_ireq_dependencies(source, dest)
diff --git a/tests/conftest.py b/tests/conftest.py
index 7cbb6814c..876d1fe7d 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -88,6 +88,10 @@ def allow_all_wheels(self):
         # No need to do an actual pip.Wheel mock here.
         yield
 
+    def copy_ireq_dependencies(self, source, dest):
+        # No state to update.
+        pass
+
 
 class FakeInstalledDistribution(object):
     def __init__(self, line, deps=None):
diff --git a/tests/test_cli_compile.py b/tests/test_cli_compile.py
index 6140efed5..5079ac2f1 100644
--- a/tests/test_cli_compile.py
+++ b/tests/test_cli_compile.py
@@ -1308,3 +1308,28 @@ def test_prefer_binary_dist_even_there_is_source_dists(
 
     assert out.exit_code == 0, out
     assert "test-package==2.0" in out.stderr.splitlines(), out.stderr
+
+
+@pytest.mark.parametrize("output_content", ("small_fake_with_deps", ""))
+def test_duplicate_reqs_combined(pip_conf, runner, output_content):
+    """
+    Test pip-compile tracks dependencies properly when install requirements are
+    combined, especially when an output file already exists.
+
+    Regression test for issue GH-1154.
+    """
+    fake_package_dir = os.path.join(PACKAGES_PATH, "small_fake_with_deps")
+    fake_package_dir = path_to_url(fake_package_dir)
+    with open("requirements.in", "w") as req_in:
+        req_in.write(fake_package_dir + "\n")
+        req_in.write(fake_package_dir + "#egg=small_fake_with_deps\n")
+
+    if output_content:
+        with open("requirements.txt", "w") as reqs_out:
+            reqs_out.write(output_content)
+
+    out = runner.invoke(cli, [])
+
+    assert out.exit_code == 0, out
+    assert fake_package_dir in out.stderr
+    assert "small-fake-a==0.1" in out.stderr
diff --git a/tests/test_repository_local.py b/tests/test_repository_local.py
index dc751177f..c0d4607c5 100644
--- a/tests/test_repository_local.py
+++ b/tests/test_repository_local.py
@@ -1,3 +1,7 @@
+import copy
+
+from tests.conftest import FakeRepository
+
 from piptools.repositories.local import LocalRequirementsRepository
 from piptools.utils import name_from_req
 
@@ -23,3 +27,25 @@ def test_get_hashes_local_repository_cache_hit(from_line, repository):
     with local_repository.allow_all_wheels():
         hashes = local_repository.get_hashes(from_line("small-fake-a==0.1"))
         assert hashes == EXPECTED
+
+
+class FakeRepositoryChecksForCopy(FakeRepository):
+    def __init__(self):
+        super(FakeRepositoryChecksForCopy, self).__init__()
+        self.copied = []
+
+    def copy_ireq_dependencies(self, source, dest):
+        self.copied.append(source)
+
+
+def test_local_repository_copy_ireq_dependencies(from_line):
+    # Ensure that local repository forwards any messages to update its state
+    # of ireq dependencies.
+    checker = FakeRepositoryChecksForCopy()
+    local_repository = LocalRequirementsRepository({}, checker)
+
+    src = from_line("small-fake-a==0.1")
+    dest = copy.deepcopy(src)
+    local_repository.copy_ireq_dependencies(src, dest)
+
+    assert src in checker.copied