diff --git a/src/documents/models.py b/src/documents/models.py
index 08f995ff6..96f027b94 100644
--- a/src/documents/models.py
+++ b/src/documents/models.py
@@ -1114,19 +1114,7 @@ class CustomFieldInstance(SoftDeleteModel):
         ]
 
     def __str__(self) -> str:
-        value = (
-            next(
-                option.get("label")
-                for option in self.field.extra_data["select_options"]
-                if option.get("id") == self.value_select
-            )
-            if (
-                self.field.data_type == CustomField.FieldDataType.SELECT
-                and self.value_select is not None
-            )
-            else self.value
-        )
-        return str(self.field.name) + f" : {value}"
+        return str(self.field.name) + f" : {self.value_for_search}"
 
     @classmethod
     def get_value_field_name(cls, data_type: CustomField.FieldDataType):
@@ -1144,6 +1132,25 @@ class CustomFieldInstance(SoftDeleteModel):
         value_field_name = self.get_value_field_name(self.field.data_type)
         return getattr(self, value_field_name)
 
+    @property
+    def value_for_search(self) -> str | None:
+        """
+        Return the value suitable for full-text indexing and display, or None
+        if the value is unset.
+
+        For SELECT fields, resolves the human-readable label rather than the
+        opaque option ID stored in value_select.
+        """
+        if self.value is None:
+            return None
+        if self.field.data_type == CustomField.FieldDataType.SELECT:
+            options = (self.field.extra_data or {}).get("select_options", [])
+            return next(
+                (o["label"] for o in options if o.get("id") == self.value),
+                None,
+            )
+        return str(self.value)
+
 
 if settings.AUDIT_LOG_ENABLED:
     auditlog.register(
diff --git a/src/documents/search/_backend.py b/src/documents/search/_backend.py
index b97957f21..f299bcd3d 100644
--- a/src/documents/search/_backend.py
+++ b/src/documents/search/_backend.py
@@ -339,14 +339,17 @@ class TantivyBackend:
         # Custom fields — JSON for structured queries (custom_fields.name:x, custom_fields.value:y),
         # companion text field for default full-text search.
         for cfi in document.custom_fields.all():
+            search_value = cfi.value_for_search
+            if search_value is None:
+                continue
             doc.add_json(
                 "custom_fields",
                 {
                     "name": cfi.field.name,
-                    "value": str(cfi.value),
+                    "value": search_value,
                 },
             )
-            doc.add_text("custom_field", str(cfi.value))
+            doc.add_text("custom_field", str(cfi))
 
         # Dates
         created_date = datetime(
@@ -513,7 +516,7 @@ class TantivyBackend:
             all_hits = [(hit[0], hit[1] / max_score) for hit in all_hits]
 
         # Apply threshold filter if configured (score-based search only)
-        threshold = getattr(settings, "ADVANCED_FUZZY_SEARCH_THRESHOLD", None)
+        threshold = settings.ADVANCED_FUZZY_SEARCH_THRESHOLD
         if threshold is not None and not sort_field:
             all_hits = [hit for hit in all_hits if hit[1] >= threshold]
 
diff --git a/src/documents/search/_query.py b/src/documents/search/_query.py
index dfa73fa50..9cde9e510 100644
--- a/src/documents/search/_query.py
+++ b/src/documents/search/_query.py
@@ -479,7 +479,7 @@ def parse_user_query(
         field_boosts=_FIELD_BOOSTS,
     )
 
-    threshold = getattr(settings, "ADVANCED_FUZZY_SEARCH_THRESHOLD", None)
+    threshold = settings.ADVANCED_FUZZY_SEARCH_THRESHOLD
     if threshold is not None:
         fuzzy = index.parse_query(
             query_str,
diff --git a/src/documents/tests/search/test_backend.py b/src/documents/tests/search/test_backend.py
index 4211611a0..12701d428 100644
--- a/src/documents/tests/search/test_backend.py
+++ b/src/documents/tests/search/test_backend.py
@@ -379,6 +379,84 @@ class TestFieldHandling:
         )
         assert results.total == 1
 
+    def test_select_custom_field_indexes_label_not_id(self, backend: TantivyBackend):
+        """SELECT custom fields must index the human-readable label, not the opaque option ID."""
+        field = CustomField.objects.create(
+            name="Category",
+            data_type=CustomField.FieldDataType.SELECT,
+            extra_data={
+                "select_options": [
+                    {"id": "opt_abc", "label": "Invoice"},
+                    {"id": "opt_def", "label": "Receipt"},
+                ],
+            },
+        )
+        doc = Document.objects.create(
+            title="Categorised doc",
+            content="test",
+            checksum="SEL1",
+            pk=71,
+        )
+        CustomFieldInstance.objects.create(
+            document=doc,
+            field=field,
+            value_select="opt_abc",
+        )
+        backend.add_or_update(doc)
+
+        # Label should be findable
+        results = backend.search(
+            "custom_fields.value:invoice",
+            user=None,
+            page=1,
+            page_size=10,
+            sort_field=None,
+            sort_reverse=False,
+        )
+        assert results.total == 1
+
+        # Opaque ID must not appear in the index
+        results = backend.search(
+            "custom_fields.value:opt_abc",
+            user=None,
+            page=1,
+            page_size=10,
+            sort_field=None,
+            sort_reverse=False,
+        )
+        assert results.total == 0
+
+    def test_none_custom_field_value_not_indexed(self, backend: TantivyBackend):
+        """Custom field instances with no value set must not produce an index entry."""
+        field = CustomField.objects.create(
+            name="Optional",
+            data_type=CustomField.FieldDataType.SELECT,
+            extra_data={"select_options": [{"id": "opt_1", "label": "Yes"}]},
+        )
+        doc = Document.objects.create(
+            title="Unset field doc",
+            content="test",
+            checksum="SEL2",
+            pk=72,
+        )
+        CustomFieldInstance.objects.create(
+            document=doc,
+            field=field,
+            value_select=None,
+        )
+        backend.add_or_update(doc)
+
+        # The string "none" must not appear as an indexed value
+        results = backend.search(
+            "custom_fields.value:none",
+            user=None,
+            page=1,
+            page_size=10,
+            sort_field=None,
+            sort_reverse=False,
+        )
+        assert results.total == 0
+
     def test_notes_include_user_information(self, backend: TantivyBackend):
         """Notes must be indexed with user information when available for structured queries."""
         user = User.objects.create_user("notewriter")