diff --git a/core/concepts/custom_validators.py b/core/concepts/custom_validators.py
index c4151eae..e6ed0165 100644
--- a/core/concepts/custom_validators.py
+++ b/core/concepts/custom_validators.py
@@ -14,6 +14,7 @@
     LOCALES_SEARCH_INDEX_TERM, INDEX_TERM, FULLY_SPECIFIED, SHORT,
     OPENMRS_CONCEPT_EXTERNAL_ID_ERROR, OPENMRS_EXTERNAL_ID_LENGTH, OPENMRS_NAME_EXTERNAL_ID_ERROR,
     OPENMRS_DESCRIPTION_EXTERNAL_ID_ERROR)
+from core.concepts.models import ConceptName
 from core.concepts.validators import BaseConceptValidator, message_with_name_details
 
 
@@ -76,7 +77,7 @@ def preferred_name_should_be_unique_for_source_and_locale(self, concept):
             concept=concept,
             attribute='locale_preferred',
             error_message=OPENMRS_PREFERRED_NAME_UNIQUE_PER_SOURCE_LOCALE,
-            filters={'names__locale_preferred': True}
+            filters={'locale_preferred': True}
         )
 
     def fully_specified_name_should_be_unique_for_source_and_locale(self, concept):
@@ -103,14 +104,20 @@ def no_other_record_has_same_name(self, name, versioned_object_id, filters=None)
         if not filters:
             filters = {}
 
-        return not self.repo.concepts_set.exclude(
-            versioned_object_id=versioned_object_id
+        # Query the localized text row directly so all name constraints apply to the same related record.
+        return not ConceptName.objects.exclude(
+            concept__versioned_object_id=versioned_object_id
         ).exclude(
-            names__type__in=(*LOCALES_SHORT, *LOCALES_SEARCH_INDEX_TERM, '', None)
+            type__in=(*LOCALES_SHORT, *LOCALES_SEARCH_INDEX_TERM, '', None)
         ).exclude(
-            names__type__isnull=True
+            type__isnull=True
         ).filter(
-            is_active=True, retired=False, is_latest_version=True, names__locale=name.locale, names__name=name.name,
+            concept__parent=self.repo,
+            concept__is_active=True,
+            concept__retired=False,
+            concept__is_latest_version=True,
+            locale=name.locale,
+            name__iexact=name.name,
             **filters
         ).exists()
 
diff --git a/core/concepts/tests/tests.py b/core/concepts/tests/tests.py
index 56d1cc06..669cc163 100644
--- a/core/concepts/tests/tests.py
+++ b/core/concepts/tests/tests.py
@@ -1800,6 +1800,51 @@ def test_concepts_should_have_unique_fully_specified_name_per_locale(self):
             }
         )
 
+    def test_duplicate_fully_specified_name_per_source_should_fail_case_insensitively_even_with_null_typed_name(self):
+        """Regression for #2406: duplicate FSNs must be rejected case-insensitively even with NULL-typed names."""
+        source = OrganizationSourceFactory(custom_validation_schema=OPENMRS_VALIDATION_SCHEMA, version=HEAD)
+
+        concept1 = Concept.persist_new(
+            {
+                'mnemonic': 'cerebral-malaria-existing',
+                'version': HEAD,
+                'parent': source,
+                'concept_class': 'Diagnosis',
+                'datatype': 'None',
+                'names': [
+                    ConceptNameFactory.build(
+                        name='Cerebral malaria', locale='en', locale_preferred=True, type='Fully Specified'
+                    ),
+                    ConceptNameFactory.build(
+                        name='Unrelated synonym with NULL type', locale='en', locale_preferred=False, type=None
+                    ),
+                ]
+            }
+        )
+        concept2 = Concept.persist_new(
+            {
+                'mnemonic': 'cerebral-malaria-duplicate',
+                'version': HEAD,
+                'parent': source,
+                'concept_class': 'Diagnosis',
+                'datatype': 'None',
+                'names': [
+                    ConceptNameFactory.build(
+                        name='cerebral malaria', locale='en', locale_preferred=True, type='Fully Specified'
+                    ),
+                ]
+            }
+        )
+
+        self.assertEqual(concept1.errors, {})
+        self.assertEqual(
+            concept2.errors,
+            {
+                'names': [OPENMRS_FULLY_SPECIFIED_NAME_UNIQUE_PER_SOURCE_LOCALE +
+                          ': cerebral malaria (locale: en, preferred: yes)']
+            }
+        )
+
     def test_at_least_one_fully_specified_name_per_concept_negative(self):
         source = OrganizationSourceFactory(custom_validation_schema=OPENMRS_VALIDATION_SCHEMA, version=HEAD)