diff --git a/src/ga4gh/va_spec/aac_2017/models.py b/src/ga4gh/va_spec/aac_2017/models.py
index 83b1566..3f83a1c 100644
--- a/src/ga4gh/va_spec/aac_2017/models.py
+++ b/src/ga4gh/va_spec/aac_2017/models.py
@@ -224,6 +224,9 @@ class VariantClinicalSignificanceStatement(
     @classmethod
     def validate_tier_evidence_lines(cls, values: dict) -> dict:
         """Validate tier I and II evidence-line types before base coercion."""
+        if not isinstance(values, dict):
+            return values
+
         classification = values.get("classification")
         if not isinstance(classification, dict):
             return values
diff --git a/tests/validation/test_va_spec_fixtures_validation.py b/tests/validation/test_va_spec_fixtures_validation.py
index ab68c08..941ae68 100644
--- a/tests/validation/test_va_spec_fixtures_validation.py
+++ b/tests/validation/test_va_spec_fixtures_validation.py
@@ -22,9 +22,15 @@
 
 
 for test_def in test_definitions:
-    if test_def["namespace"].startswith("va-spec."):
-        schema = get_va_spec_schema(test_def["namespace"].split("va-spec.")[-1])
-        VA_SPEC_TEST_DEFINITIONS[schema].append(test_def)
+    namespace = test_def["namespace"]
+    # Base (core) fixtures use the namespace ``va-spec``; profiles use
+    # ``va-spec.<profile>``. Anything else (e.g. ``vrs``) is out of scope.
+    if namespace != "va-spec" and not namespace.startswith("va-spec."):
+        continue
+    schema = get_va_spec_schema(namespace.split("va-spec.")[-1])
+    if schema is None:
+        continue
+    VA_SPEC_TEST_DEFINITIONS[schema].append(test_def)
 
 
 def test_va_spec_fixtures():