diff --git a/src/specify_cli/bundles/catalog_config.py b/src/specify_cli/bundles/catalog_config.py
index db1833a4ca..7a8bcd7174 100644
--- a/src/specify_cli/bundles/catalog_config.py
+++ b/src/specify_cli/bundles/catalog_config.py
@@ -110,7 +110,10 @@ def _canonicalize_url(url: str) -> str:
 
     Remote URLs (``http(s)://``, ``file://``, ``builtin://``) are returned
     unchanged; only bare/relative local paths are resolved to an absolute path.
+    Foreign Windows drive paths stay unchanged rather than becoming POSIX paths.
     """
+    if _WINDOWS_DRIVE_RE.match(url) and not Path(url).is_absolute():
+        return url
     if _is_local_path(url):
         return str(Path(url).expanduser().resolve())
     return url
diff --git a/tests/specify_cli/bundles/test_catalog_config.py b/tests/specify_cli/bundles/test_catalog_config.py
index 19fc79b37a..2df4cc921b 100644
--- a/tests/specify_cli/bundles/test_catalog_config.py
+++ b/tests/specify_cli/bundles/test_catalog_config.py
@@ -1,6 +1,7 @@
 """Unit tests for project catalog-config id derivation and url canonicalization."""
 from __future__ import annotations
 
+import os
 from pathlib import Path
 
 import pytest
@@ -72,6 +73,28 @@ def test_add_source_persists_absolute_local_path(tmp_path: Path, monkeypatch):
     assert Path(source.url) == catalog.resolve()
 
 
+@pytest.mark.skipif(os.name == "nt", reason="POSIX path rewriting regression")
+@pytest.mark.parametrize("url", [r"C:\catalog.json", "C:/catalog.json"])
+def test_add_source_preserves_foreign_windows_drive_path(tmp_path: Path, url: str):
+    project = tmp_path / "proj"
+    project.mkdir()
+
+    source, status = cc.add_source(
+        project, url, policy="install-allowed", priority=50
+    )
+
+    assert status == "added"
+    assert source.url == url
+    assert cc._read(project)[0]["url"] == url
+    repeated, status = cc.add_source(
+        project, url, policy="install-allowed", priority=50
+    )
+    assert status == "unchanged"
+    assert repeated.url == url
+    cc.remove_source(project, url)
+    assert cc._read(project) == []
+
+
 def test_add_source_normalizes_existing_entry_for_idempotency(tmp_path: Path):
     project = tmp_path / "proj"
     (project / ".specify").mkdir(parents=True)