diff --git a/api/app/Console/Commands/VerifyFormsDataIntegrity.php b/api/app/Console/Commands/VerifyFormsDataIntegrity.php
index 6eddb4f1..543cf39e 100644
--- a/api/app/Console/Commands/VerifyFormsDataIntegrity.php
+++ b/api/app/Console/Commands/VerifyFormsDataIntegrity.php
@@ -259,19 +259,15 @@ final class VerifyFormsDataIntegrity extends Command
             ])
             ->count();
 
-        if ($orphanSub > 0 || $orphanField > 0 || $dup > 0 || $longIndexed > 0 || $multiValueIndexed > 0) {
+        if ($orphanSub > 0 || $orphanField > 0 || $dup > 0 || $longIndexed > 0 || $multiValueIndexed > 0 || $nonFilterableIndexed > 0) {
             $this->recordFailure('Value coherence',
-                "{$orphanSub} orphan submission, {$orphanField} orphan field, {$dup} duplicate pairs, {$longIndexed} over-length value_indexed, {$multiValueIndexed} multi-value rows with value_indexed set"
+                "{$orphanSub} orphan submission, {$orphanField} orphan field, {$dup} duplicate pairs, {$longIndexed} over-length value_indexed, {$multiValueIndexed} multi-value rows with value_indexed set, {$nonFilterableIndexed} value_indexed set on non-filterable field",
+                'observer should only populate value_indexed when field.is_filterable=true — re-save affected rows to let FormValueObserver reconcile'
             );
 
             return;
         }
 
-        // Warning only — doesn't fail the check.
-        if ($nonFilterableIndexed > 0) {
-            $this->warn("  [WARN] {$nonFilterableIndexed} form_values have value_indexed set for a non-filterable field");
-        }
-
         $this->recordPass('Value coherence', "{$total} values verified");
     }
 
diff --git a/api/app/Observers/FormBuilder/FormValueObserver.php b/api/app/Observers/FormBuilder/FormValueObserver.php
index 4b8b47ee..424d1504 100644
--- a/api/app/Observers/FormBuilder/FormValueObserver.php
+++ b/api/app/Observers/FormBuilder/FormValueObserver.php
@@ -36,24 +36,23 @@ final class FormValueObserver
         $this->resetTypedColumns($value);
 
         // value stores the canonical payload (always JSON). Typed columns
-        // are derived from it based on the field's storage hint.
+        // are derived from it per field.value_storage_hint, with one
+        // exception: value_indexed is filter-driven (§4.4), not hint-driven,
+        // so populate it ONLY when field.is_filterable = true. Keeps the
+        // partial index lean and simplifies FilterQueryBuilder (S4).
         $raw = $value->value;
         $scalar = $this->extractScalar($raw);
 
         match ($field->value_storage_hint) {
-            FormValueStorageHint::STRING => $value->value_indexed = $this->truncateIndexed($scalar),
+            FormValueStorageHint::STRING => null, // handled below, filter-gated
             FormValueStorageHint::NUMBER => $value->value_number = is_numeric($scalar) ? (float) $scalar : null,
             FormValueStorageHint::DATE => $value->value_date = $this->castDate($scalar),
             FormValueStorageHint::BOOL => $value->value_bool = $scalar === null ? null : (bool) $scalar,
             FormValueStorageHint::JSON => null,
         };
 
-        // Single-value filterable fields: ensure value_indexed is populated
-        // regardless of storage hint, so filter queries hit one index.
         if ($field->is_filterable && ! $this->isMultiValueType($field)) {
-            if ($value->value_indexed === null) {
-                $value->value_indexed = $this->truncateIndexed($scalar);
-            }
+            $value->value_indexed = $this->truncateIndexed($scalar);
         }
     }
 
diff --git a/api/tests/Unit/Observers/FormBuilder/FormValueObserverTest.php b/api/tests/Unit/Observers/FormBuilder/FormValueObserverTest.php
index 7bf0ffce..d0394ef1 100644
--- a/api/tests/Unit/Observers/FormBuilder/FormValueObserverTest.php
+++ b/api/tests/Unit/Observers/FormBuilder/FormValueObserverTest.php
@@ -32,11 +32,12 @@ final class FormValueObserverTest extends TestCase
         ]);
     }
 
-    public function test_string_hint_populates_value_indexed(): void
+    public function test_string_hint_populates_value_indexed_when_filterable(): void
     {
         $field = FormField::factory()->for($this->schema, 'schema')->create([
             'field_type' => FormFieldType::TEXT->value,
             'value_storage_hint' => FormValueStorageHint::STRING,
+            'is_filterable' => true,
         ]);
 
         $value = FormValue::create([
@@ -51,6 +52,23 @@ final class FormValueObserverTest extends TestCase
         $this->assertNull($value->value_bool);
     }
 
+    public function test_string_hint_leaves_value_indexed_null_when_not_filterable(): void
+    {
+        $field = FormField::factory()->for($this->schema, 'schema')->create([
+            'field_type' => FormFieldType::TEXT->value,
+            'value_storage_hint' => FormValueStorageHint::STRING,
+            'is_filterable' => false,
+        ]);
+
+        $value = FormValue::create([
+            'form_submission_id' => $this->submission->id,
+            'form_field_id' => $field->id,
+            'value' => ['value' => 'Niet-filterable tekst'],
+        ]);
+
+        $this->assertNull($value->fresh()->value_indexed);
+    }
+
     public function test_number_hint_populates_value_number(): void
     {
         $field = FormField::factory()->for($this->schema, 'schema')->create([