diff --git a/app/routes/thematic/geoencoder.py b/app/routes/thematic/geoencoder.py
index 8dcb4dc8..4e5aa5ba 100644
--- a/app/routes/thematic/geoencoder.py
+++ b/app/routes/thematic/geoencoder.py
@@ -116,6 +116,9 @@ def sanitize_names(
     region: str | None,
     subregion: str | None,
 ) -> List[str | None]:
+    """Turn any empty strings into Nones, enforce the admin level hierarchy,
+    and optionally unaccent names.
+    """
     names = []
 
     if subregion and not region:
@@ -137,6 +140,9 @@ def sanitize_names(
 def determine_admin_level(
     country: str | None, region: str | None, subregion: str | None
 ) -> str:
+    """Infer the native admin level of a request based on the presence of
+    non-empty fields
+    """
     if subregion:
         return "2"
     elif region:
@@ -182,7 +188,11 @@ async def version_is_valid(
     dataset: str,
     version: str,
 ) -> None:
-    """ """
+    """Validate a version string for a given dataset."""
+    # Note: At some point I intend to change the version validator to
+    # use messaging like this. However, that is out of scope for the
+    # current ticket, and I want to see what people think, so I'll
+    # keep it here for now.
     if re.match(VERSION_REGEX, version) is None:
         raise HTTPException(
             status_code=400,
@@ -200,6 +210,7 @@ async def version_is_valid(
             status_code=400,
             detail=(
                 "Version not found. Existing versions for this dataset "
-                f"include {await get_version_names(dataset)}"
+                f"include {[v[0] for v in await get_version_names(dataset)]}"
+                # FIXME: Maybe change get_version_names to do unpacking? ^
             ),
         )
diff --git a/tests_v2/unit/app/routes/thematic/geoencoder/test_geoencoder.py b/tests_v2/unit/app/routes/thematic/geoencoder/test_geoencoder.py
index 6a2ec249..14e30b99 100644
--- a/tests_v2/unit/app/routes/thematic/geoencoder/test_geoencoder.py
+++ b/tests_v2/unit/app/routes/thematic/geoencoder/test_geoencoder.py
@@ -4,6 +4,7 @@
 from httpx import AsyncClient
 
 from app.models.pydantic.geostore import GeostoreCommon
+from app.routes.datasets.versions import get_version
 from app.routes.thematic import geoencoder
 from app.routes.thematic.geoencoder import _admin_boundary_lookup_sql
 
@@ -75,7 +76,7 @@ async def test_geoencoder_invalid_version_pattern(async_client: AsyncClient) ->
 
     resp = await async_client.get("/thematic/geoencode", params=params)
 
-    assert resp.json().get("message", {}).startswith("Invalid version")
+    assert resp.json().get("message", {}).startswith("Invalid version name")
     assert resp.status_code == 400
 
 
@@ -89,6 +90,22 @@ async def test_geoencoder_nonexistant_version(async_client: AsyncClient) -> None
     assert resp.status_code == 400
 
 
+@pytest.mark.asyncio
+async def test_geoencoder_nonexistant_version_lists_existing(
+    async_client: AsyncClient, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    async def mock_get_version_names(dataset: str):
+        return [("fdkj",), ("dslj",), ("kfj",)]
+
+    monkeypatch.setattr(geoencoder, "get_version_names", mock_get_version_names)
+
+    params = {"country": "Canada", "admin_version": "v4.0"}
+    resp = await async_client.get("/thematic/geoencode", params=params)
+
+    assert resp.json().get("message", {}).endswith("['fdkj', 'dslj', 'kfj']")
+    assert resp.status_code == 400
+
+
 @pytest.mark.asyncio
 async def test_geoencoder_bad_boundary_source(async_client: AsyncClient) -> None:
     params = {