diff --git a/tests/test_cli.py b/tests/test_cli.py
index dd299553..e7c1af14 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -691,3 +691,135 @@ def fake_env_name_to_prefix(
     # Optionally, verify that our fake function printed the expected message.
     output = capsys.readouterr().out
     assert "Fake create called with" in output
+
+
+def test_no_duplicate_local_dependencies_in_install_command(tmp_path: Path) -> None:
+    """Test that local dependencies are not duplicated in the pip install command.
+
+    This test reproduces the issue where the same local dependency appears
+    multiple times in the pip install command when it's referenced by multiple
+    projects.
+    """
+    # Create a shared local dependency that will be referenced multiple times
+    shared_dep = tmp_path / "shared_dependency"
+    shared_dep.mkdir()
+    (shared_dep / "setup.py").write_text(
+        textwrap.dedent(
+            """\
+            from setuptools import setup
+            setup(name="shared_dep", version="0.1.0")
+            """,
+        ),
+    )
+
+    # Create multiple projects that all reference the same shared dependency
+    projects = []
+    for i in range(3):
+        project = tmp_path / f"project_{i}"
+        project.mkdir()
+
+        # Create a requirements.yaml that references the shared dependency
+        (project / "requirements.yaml").write_text(
+            textwrap.dedent(
+                f"""\
+                name: project_{i}
+                dependencies:
+                    - numpy
+                local_dependencies:
+                    - ../shared_dependency
+                """,
+            ),
+        )
+
+        # Create a minimal setup.py to make it pip installable
+        (project / "setup.py").write_text(
+            textwrap.dedent(
+                f"""\
+                from setuptools import setup
+                setup(name="project_{i}", version="0.1.0")
+                """,
+            ),
+        )
+
+        projects.append(project / "requirements.yaml")
+
+    # Mock subprocess.run to capture the pip install commands
+    pip_install_commands = []
+
+    def mock_run(cmd, *args, **kwargs):
+        # Capture pip install commands with -e flags
+        if isinstance(cmd, list) and "pip" in str(cmd) and "install" in cmd:
+            # Look for -e flags in the command
+            editable_packages = []
+            i = 0
+            while i < len(cmd):
+                if cmd[i] == "-e" and i + 1 < len(cmd):
+                    editable_packages.append(cmd[i + 1])
+                    i += 2
+                else:
+                    i += 1
+            if editable_packages:
+                pip_install_commands.append(editable_packages)
+
+        # Don't actually run the command in tests
+        from unittest.mock import MagicMock
+
+        result = MagicMock()
+        result.returncode = 0
+        return result
+
+    import warnings
+
+    with patch("subprocess.run", side_effect=mock_run):
+        # Run the install command with all projects
+        # Expect a warning about unmanaged local dependency
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore", UserWarning)
+            _install_command(
+                *projects,
+                conda_executable=None,
+                conda_env_name=None,
+                conda_env_prefix=None,
+                conda_lock_file=None,
+                dry_run=False,
+                editable=True,
+                skip_local=False,
+                skip_pip=True,  # Skip regular pip deps to focus on local deps
+                skip_conda=True,  # Skip conda deps
+                no_dependencies=False,
+                ignore_pins=None,
+                overwrite_pins=None,
+                skip_dependencies=None,
+                no_uv=True,
+                verbose=False,
+            )
+
+    # Check that the shared dependency appears only once in pip install commands
+    all_editable_packages = []
+    for packages in pip_install_commands:
+        all_editable_packages.extend(packages)
+
+    # Count how many times the shared_dependency appears
+    shared_dep_str = str(shared_dep.resolve())
+    shared_dep_count = sum(
+        1 for pkg in all_editable_packages if str(Path(pkg).resolve()) == shared_dep_str
+    )
+
+    # The shared dependency should appear exactly once, not multiple times
+    assert shared_dep_count == 1, (
+        f"Expected shared_dependency to appear once in pip install command, "
+        f"but it appeared {shared_dep_count} times. "
+        f"All editable packages: {all_editable_packages}"
+    )
+
+    # Also check that each project appears exactly once
+    for i in range(3):
+        project_path = str((tmp_path / f"project_{i}").resolve())
+        project_count = sum(
+            1
+            for pkg in all_editable_packages
+            if str(Path(pkg).resolve()) == project_path
+        )
+        assert project_count == 1, (
+            f"Expected project_{i} to appear once, but it appeared {project_count} times"
+        )
diff --git a/unidep/_cli.py b/unidep/_cli.py
index e820d6e1..32fef3e9 100755
--- a/unidep/_cli.py
+++ b/unidep/_cli.py
@@ -1065,12 +1065,12 @@ def _install_command(  # noqa: PLR0912, PLR0915
         names = {k.name: [dep.name for dep in v] for k, v in local_dependencies.items()}
         print(f"📝 Found local dependencies: {names}\n")
         installable_set = {p.resolve() for p in installable}
-        installable += [
-            dep
-            for deps in local_dependencies.values()
-            for dep in deps
-            if dep.resolve() not in installable_set
-        ]
+        for deps in local_dependencies.values():
+            for dep in deps:
+                dep_resolved = dep.resolve()
+                if dep_resolved not in installable_set:
+                    installable.append(dep)
+                    installable_set.add(dep_resolved)
         if installable:
             pip_flags = ["--no-deps"]  # we just ran pip/conda install, so skip
             if verbose: