diff --git a/mapillary_tools/geotag/factory.py b/mapillary_tools/geotag/factory.py
index dc9d21e25..3a3d975f7 100644
--- a/mapillary_tools/geotag/factory.py
+++ b/mapillary_tools/geotag/factory.py
@@ -10,6 +10,8 @@
 import typing as T
 from pathlib import Path
 
+import jsonschema
+
 from .. import exceptions, types, utils
 from . import (
     base,
@@ -50,6 +52,9 @@ def parse_source_option(source: str) -> list[SourceOption]:
         "gpx,exif" -> [SourceOption(SourceType.GPX), SourceOption(SourceType.EXIF)]
         "exif,gpx" -> [SourceOption(SourceType.EXIF), SourceOption(SourceType.GPX)]
         '{"source": "gpx"}' -> [SourceOption(SourceType.GPX)]
+
+    Raise MapillaryBadParameterError for an unknown source type, and for a
+    JSON object that does not match SourceOptionSchema.
     """
 
     try:
@@ -64,11 +69,27 @@ def parse_source_option(source: str) -> list[SourceOption]:
     except json.JSONDecodeError:
         pass
     else:
-        return [SourceOption.from_dict(payload)]
+        try:
+            return [SourceOption.from_dict(payload)]
+        except jsonschema.ValidationError as ex:
+            raise exceptions.MapillaryBadParameterError(
+                f"Invalid geotag source {source}: {ex.message}"
+            ) from ex
 
     sources = source.split(",")
 
-    return [SourceOption(SourceType(SOURCE_TYPE_ALIAS.get(s, s))) for s in sources]
+    return [SourceOption(_parse_source_type(s)) for s in sources]
+
+
+def _parse_source_type(source: str) -> SourceType:
+    try:
+        return SourceType(SOURCE_TYPE_ALIAS.get(source, source))
+    except ValueError:
+        raise exceptions.MapillaryBadParameterError(
+            f"Invalid geotag source {source!r}. Supported source types: "
+            f"{', '.join(s.value for s in SourceType)} "
+            f"(aliases: {', '.join(SOURCE_TYPE_ALIAS)})"
+        ) from None
 
 
 def parse_source_options(
diff --git a/tests/unit/test_parse_source_option.py b/tests/unit/test_parse_source_option.py
new file mode 100644
index 000000000..c3412f50e
--- /dev/null
+++ b/tests/unit/test_parse_source_option.py
@@ -0,0 +1,68 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the BSD license found in the
+# LICENSE file in the root directory of this source tree.
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from mapillary_tools import exceptions, sample_video
+from mapillary_tools.geotag.factory import parse_source_option, parse_source_options
+from mapillary_tools.geotag.options import SourceType
+
+
+class TestParseSourceOption:
+    def test_source_types(self):
+        assert [o.source for o in parse_source_option("gpx")] == [SourceType.GPX]
+        assert [o.source for o in parse_source_option("gopro_videos")] == [
+            SourceType.GOPRO
+        ]
+        assert [o.source for o in parse_source_option("exif,native")] == [
+            SourceType.EXIF,
+            SourceType.NATIVE,
+        ]
+        assert [o.source for o in parse_source_option('{"source": "nmea"}')] == [
+            SourceType.NMEA
+        ]
+
+    @pytest.mark.parametrize("source", ["foo", "gpx,foo", "foo,gpx"])
+    def test_unknown_source_type_names_the_supported_ones(self, source):
+        with pytest.raises(exceptions.MapillaryBadParameterError) as excinfo:
+            parse_source_option(source)
+
+        message = str(excinfo.value)
+        assert "'foo'" in message
+        assert ", ".join(s.value for s in SourceType) in message
+        assert "(aliases: blackvue_videos, gopro_videos, exiftool)" in message
+
+    def test_unknown_key_is_named(self):
+        with pytest.raises(exceptions.MapillaryBadParameterError) as excinfo:
+            parse_source_option('{"source": "gpx", "path": "track.gpx"}')
+
+        assert "'path' was unexpected" in str(excinfo.value)
+
+    @pytest.mark.parametrize(
+        "source",
+        [
+            '{"source": "foo"}',
+            '{"path": "track.gpx"}',
+            '{"source": "gpx", "filetypes": ["mp4"]}',
+            '{"source": "gpx", "interpolation_offset_time": "1s"}',
+            "123",
+        ],
+    )
+    def test_invalid_json_source(self, source):
+        with pytest.raises(exceptions.MapillaryBadParameterError):
+            parse_source_option(source)
+
+    def test_video_geotag_source(self):
+        with pytest.raises(exceptions.MapillaryBadParameterError):
+            parse_source_options(
+                geotag_source=[], video_geotag_source=["foo"], geotag_source_path=None
+            )
+
+    def test_video_process(self, tmp_path: Path):
+        with pytest.raises(exceptions.MapillaryBadParameterError):
+            sample_video._parse_video_sources(["foo"], None, None, tmp_path)