diff --git a/marimo/_cli/sandbox.py b/marimo/_cli/sandbox.py
index d1212d805f5..06e8aacf216 100644
--- a/marimo/_cli/sandbox.py
+++ b/marimo/_cli/sandbox.py
@@ -132,6 +132,15 @@ def _is_versioned(dependency: str) -> bool:
     return any(c in dependency for c in ("==", ">=", "<=", ">", "<", "~"))
 
 
+def _requirement_name(requirement: str) -> str:
+    """Bare package name, lowercased. Enough to detect duplicates."""
+    token = requirement.strip().split(";", 1)[0].split("#", 1)[0]
+    token = token.split("[", 1)[0]
+    for spec in ("===", "==", ">=", "<=", "~=", "!=", ">", "<"):
+        token = token.split(spec, 1)[0]
+    return token.split("@", 1)[0].strip().lower()
+
+
 def _normalize_sandbox_dependencies(
     dependencies: list[str],
     marimo_version: str,
@@ -570,15 +579,14 @@ def get_sandbox_requirements(
         dependencies, __version__, additional_features=[]
     )
 
-    # Add additional deps if not already present
     if additional_deps:
-        existing_lower = {
-            d.lower().split("[")[0].split(">=")[0].split("==")[0]
-            for d in normalized
-        }
+        existing = {_requirement_name(dep) for dep in normalized}
+        existing.discard("")
         for dep in additional_deps:
-            if dep.lower() not in existing_lower:
+            name = _requirement_name(dep)
+            if name and name not in existing:
                 normalized.append(dep)
+                existing.add(name)
 
     return normalized
 
diff --git a/marimo/_session/_venv.py b/marimo/_session/_venv.py
index 6a00b8641c1..06a521fba59 100644
--- a/marimo/_session/_venv.py
+++ b/marimo/_session/_venv.py
@@ -14,7 +14,6 @@
 import os
 import subprocess
 import sys
-from importlib.metadata import version
 from pathlib import Path
 from typing import TYPE_CHECKING
 
@@ -30,17 +29,12 @@
 
 
 def get_ipc_kernel_deps() -> list[str]:
-    """Get dependencies required for IPC kernel communication.
+    """Dependencies the sandbox kernel needs for host IPC.
 
-    Returns pyzmq pinned to the currently installed version to ensure
-    compatibility between host and sandbox environments.
+    A lower bound, not a host pin. The notebook lock may already have
+    pyzmq at another version, and ZMQ does not require an exact match.
     """
-    try:
-        pyzmq_version = version("pyzmq")
-        return [f"pyzmq=={pyzmq_version}"]
-    except Exception:
-        # Fallback if pyzmq not installed
-        return ["pyzmq>=27.1.0"]
+    return ["pyzmq>=27.1.0"]
 
 
 def _find_python_in_venv(venv_path: str) -> str | None:
diff --git a/tests/_cli/test_sandbox.py b/tests/_cli/test_sandbox.py
index 9059dc2030e..3eae9dd80e0 100644
--- a/tests/_cli/test_sandbox.py
+++ b/tests/_cli/test_sandbox.py
@@ -12,6 +12,7 @@
     _ensure_marimo_in_script_metadata,
     _ensure_python_version_in_script_metadata,
     _normalize_sandbox_dependencies,
+    _requirement_name,
     build_sandbox_venv,
     cleanup_sandbox_dir,
     construct_uv_command,
@@ -784,6 +785,52 @@ def test_get_sandbox_requirements_none_filename() -> None:
     assert "pyzmq" in reqs
 
 
+def test_requirement_name_strips_specifiers_and_markers() -> None:
+    assert _requirement_name("pyzmq==27.1.0") == "pyzmq"
+    assert (
+        _requirement_name(
+            "pyzmq==27.2.0 ; python_full_version < '3.15' "
+            "and sys_platform != 'emscripten'"
+        )
+        == "pyzmq"
+    )
+    assert _requirement_name("marimo[lsp]>=0.24.0") == "marimo"
+
+
+def test_get_sandbox_requirements_skips_additional_dep_already_present(
+    tmp_path: Path,
+) -> None:
+    """Do not add a second pyzmq pin next to the uv-export lock line."""
+    from marimo._cli.sandbox import get_sandbox_requirements
+
+    script_path = tmp_path / "test.py"
+    script_path.write_text(
+        """# /// script
+# dependencies = ["marimo>=0.24.0"]
+# ///
+import marimo
+"""
+    )
+    exported_pyzmq = (
+        "pyzmq==27.2.0 ; python_full_version < '3.15' "
+        "and sys_platform != 'emscripten'"
+    )
+
+    with (
+        patch("marimo._cli.sandbox.is_editable", return_value=False),
+        patch(
+            "marimo._cli.sandbox._resolve_requirements_txt_lines",
+            return_value=["marimo==0.24.0", exported_pyzmq],
+        ),
+    ):
+        reqs = get_sandbox_requirements(
+            str(script_path),
+            additional_deps=["pyzmq>=27.1.0"],
+        )
+
+    assert reqs == [exported_pyzmq, "marimo==0.24.0"]
+
+
 def test_cleanup_sandbox_dir_removes_directory(tmp_path: Path) -> None:
     """Test that cleanup_sandbox_dir removes the directory."""
     from marimo._cli.sandbox import cleanup_sandbox_dir
diff --git a/tests/_session/test_venv.py b/tests/_session/test_venv.py
index f8adf717f6f..dd4a9694af6 100644
--- a/tests/_session/test_venv.py
+++ b/tests/_session/test_venv.py
@@ -12,11 +12,16 @@
 from marimo._session._venv import (
     check_python_version_compatibility,
     get_configured_venv_python,
+    get_ipc_kernel_deps,
     get_kernel_pythonpath,
     has_marimo_installed,
 )
 
 
+def test_get_ipc_kernel_deps_is_a_lower_bound() -> None:
+    assert get_ipc_kernel_deps() == ["pyzmq>=27.1.0"]
+
+
 def test_get_configured_venv_python_returns_none_when_not_configured() -> None:
     """Test returns None when venv not in config."""
     config: dict[str, Any] = {}  # No venv configured