diff --git a/phpstan-baseline.php b/phpstan-baseline.php
index f0a882e68b01..c48093046742 100644
--- a/phpstan-baseline.php
+++ b/phpstan-baseline.php
@@ -10459,12 +10459,6 @@
 	'count' => 1,
 	'path' => __DIR__ . '/system/Validation/Validation.php',
 ];
-$ignoreErrors[] = [
-	// identifier: missingType.iterableValue
-	'message' => '#^Property CodeIgniter\\\\Validation\\\\Validation\\:\\:\\$rules type has no value type specified in iterable type array\\.$#',
-	'count' => 1,
-	'path' => __DIR__ . '/system/Validation/Validation.php',
-];
 $ignoreErrors[] = [
 	// identifier: missingType.iterableValue
 	'message' => '#^Property CodeIgniter\\\\Validation\\\\Validation\\:\\:\\$validated type has no value type specified in iterable type array\\.$#',
diff --git a/system/Validation/Validation.php b/system/Validation/Validation.php
index bfc661c2b3d4..a4d817d2a9b4 100644
--- a/system/Validation/Validation.php
+++ b/system/Validation/Validation.php
@@ -51,7 +51,7 @@ class Validation implements ValidationInterface
     /**
      * Stores the actual rules that should be run against $data.
      *
-     * @var array
+     * @var array<array-key, array{label?: string, rules: list<string>}>
      *
      * [
      *     field1 => [
@@ -163,6 +163,9 @@ public function run(?array $data = null, ?string $group = null, $dbGroup = null)
         // Run through each rule. If we have any field set for
         // this rule, then we need to run them through!
         foreach ($this->rules as $field => $setup) {
+            //  An array key might be int.
+            $field = (string) $field;
+
             $rules = $setup['rules'];
 
             if (is_string($rules)) {
diff --git a/tests/system/Validation/ValidationTest.php b/tests/system/Validation/ValidationTest.php
index b5493a682c8e..00360f368e66 100644
--- a/tests/system/Validation/ValidationTest.php
+++ b/tests/system/Validation/ValidationTest.php
@@ -270,6 +270,16 @@ public function testRunDoesTheBasics(): void
         $this->assertSame([], $this->validation->getValidated());
     }
 
+    public function testRunWithNumericFieldName(): void
+    {
+        // The array key will be int.
+        $data = ['123' => 'notanumber'];
+        $this->validation->setRules(['123' => 'is_numeric']);
+
+        $this->assertFalse($this->validation->run($data));
+        $this->assertSame([], $this->validation->getValidated());
+    }
+
     public function testClosureRule(): void
     {
         $this->validation->setRules(