diff --git a/rules-tests/Php85/Rector/ArrayDimFetch/ArrayFirstLastRector/Fixture/skip_under_unset.php.inc b/rules-tests/Php85/Rector/ArrayDimFetch/ArrayFirstLastRector/Fixture/skip_under_unset.php.inc
new file mode 100644
index 00000000000..e6e23429a2c
--- /dev/null
+++ b/rules-tests/Php85/Rector/ArrayDimFetch/ArrayFirstLastRector/Fixture/skip_under_unset.php.inc
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\Php85\Rector\ArrayDimFetch\ArrayFirstLastRector\Fixture;
+
+final class SkipUnderUnset
+{
+    public function run()
+    {
+        $a = [1,2,3];
+        unset($a[array_key_last($a)]);
+    }
+}
diff --git a/rules/Php85/Rector/ArrayDimFetch/ArrayFirstLastRector.php b/rules/Php85/Rector/ArrayDimFetch/ArrayFirstLastRector.php
index ff4114a440d..0a9e21f563c 100644
--- a/rules/Php85/Rector/ArrayDimFetch/ArrayFirstLastRector.php
+++ b/rules/Php85/Rector/ArrayDimFetch/ArrayFirstLastRector.php
@@ -7,6 +7,7 @@
 use PhpParser\Node;
 use PhpParser\Node\Expr\ArrayDimFetch;
 use PhpParser\Node\Expr\FuncCall;
+use Rector\NodeTypeResolver\Node\AttributeKey;
 use Rector\PHPStan\ScopeFetcher;
 use Rector\Rector\AbstractRector;
 use Rector\ValueObject\PhpVersionFeature;
@@ -88,6 +89,10 @@ public function refactor(Node $node): ?FuncCall
             return null;
         }
 
+        if ($node->getAttribute(AttributeKey::IS_UNSET_VAR)) {
+            return null;
+        }
+
         $functionName = $this->isName($node->dim, self::ARRAY_KEY_FIRST)
             ? 'array_first'
             : 'array_last';