diff --git a/src/dgbowl_schemas/yadg/dataschema_5_1/__init__.py b/src/dgbowl_schemas/yadg/dataschema_5_1/__init__.py
index 95073a5..1591d3b 100644
--- a/src/dgbowl_schemas/yadg/dataschema_5_1/__init__.py
+++ b/src/dgbowl_schemas/yadg/dataschema_5_1/__init__.py
@@ -20,7 +20,7 @@ class DataSchema(BaseModel, extra="forbid"):
     metadata: Optional[Mapping[str, Any]]
     """Input metadata for :mod:`yadg`."""
 
-    step_defaults: StepDefaults = Field(StepDefaults())
+    step_defaults: StepDefaults = Field(..., default_factory=StepDefaults)
     """Default values for configuration of each :class:`Step`."""
 
     steps: Sequence[Step]
diff --git a/src/dgbowl_schemas/yadg/dataschema_5_1/filetype.py b/src/dgbowl_schemas/yadg/dataschema_5_1/filetype.py
index 91cbe38..e91da8d 100644
--- a/src/dgbowl_schemas/yadg/dataschema_5_1/filetype.py
+++ b/src/dgbowl_schemas/yadg/dataschema_5_1/filetype.py
@@ -33,11 +33,14 @@ def timezone_resolve_localtime(cls, v):
     @field_validator("locale")
     @classmethod
     def locale_set_default(cls, v):
-        if v is None:
-            v = locale.getlocale(locale.LC_NUMERIC)[0]
-        try:
-            v = str(Locale.parse(v))
-        except (TypeError, UnknownLocaleError):
+        for loc in (v, locale.getlocale(locale.LC_NUMERIC)[0], locale.getlocale()[0]):
+            try:
+                v = str(Locale.parse(loc))
+                break
+            except (TypeError, UnknownLocaleError, ValueError) as e:
+                logger.debug("Could not process locale '%s': %s", loc, e)
+        else:
+            logger.debug("No valid locale string provided. Defaulting to 'en_GB'.")
             v = "en_GB"
         return v
 
diff --git a/src/dgbowl_schemas/yadg/dataschema_5_1/stepdefaults.py b/src/dgbowl_schemas/yadg/dataschema_5_1/stepdefaults.py
index 66b9a79..3161cee 100644
--- a/src/dgbowl_schemas/yadg/dataschema_5_1/stepdefaults.py
+++ b/src/dgbowl_schemas/yadg/dataschema_5_1/stepdefaults.py
@@ -3,6 +3,9 @@
 import locale
 from babel import Locale, UnknownLocaleError
 import tzlocal
+import logging
+
+logger = logging.getLogger(__name__)
 
 
 class StepDefaults(BaseModel, extra="forbid"):
@@ -39,8 +42,9 @@ def locale_set_default(cls, v):
             try:
                 v = str(Locale.parse(loc))
                 break
-            except (TypeError, UnknownLocaleError):
-                pass
+            except (TypeError, UnknownLocaleError, ValueError) as e:
+                logger.debug("Could not process locale '%s': %s", loc, e)
         else:
+            logger.debug("No valid locale string provided. Defaulting to 'en_GB'.")
             v = "en_GB"
         return v
diff --git a/tests/test_dataschema.py b/tests/test_dataschema.py
index 1b76e90..0c8f832 100644
--- a/tests/test_dataschema.py
+++ b/tests/test_dataschema.py
@@ -170,3 +170,24 @@ def test_extractor_factory(input, output):
     assert ret.locale == output.get("locale")
     assert ret.encoding == output.get("encoding")
     assert ret.timezone is not None
+
+
+@pytest.mark.parametrize(
+    "input, output",
+    [
+        ("en_GB", "en_GB"),
+        ("en_US", "en_US"),
+        ("en_US.UTF-8", "en_US"),  # check parsing with .UTF-8 suffix
+        ("de_DE.windows-1252", "de_DE"),  # check parsing with .windows-1252 suffix
+        # Failures defaulting to en_GB below here
+        ("en-US", "en_GB"),  # check that parsing with "-" fails
+        ("no_NO", "en_GB"),  # no_NO is not a valid locale, nb_NO is
+        ("English_United States", "en_GB"),  # English_United States is a language
+        ("English (United States)", "en_GB"),  # English (United States) is a language
+        ("Norwegian (Bokmål)", "en_GB"),  # Norwegian (Bokmål) is a language
+        (None, "en_GB"),  # Full fallback.
+    ],
+)
+def test_stepdefaults_locale(input, output):
+    ret = ExtractorFactory(extractor=dict(filetype="example", locale=input)).extractor
+    assert ret.locale == output