diff --git a/rules-tests/Php85/Rector/FuncCall/ArrayKeyExistsNullToEmptyStringRector/Fixture/skip_defined_int_or_string.php.inc b/rules-tests/Php85/Rector/FuncCall/ArrayKeyExistsNullToEmptyStringRector/Fixture/skip_defined_int_or_string.php.inc
new file mode 100644
index 00000000000..45222b039b5
--- /dev/null
+++ b/rules-tests/Php85/Rector/FuncCall/ArrayKeyExistsNullToEmptyStringRector/Fixture/skip_defined_int_or_string.php.inc
@@ -0,0 +1,23 @@
+<?php
+
+namespace Rector\Tests\Php85\Rector\FuncCall\ArrayKeyExistsNullToEmptyStringRector\Fixture;
+
+final class SkipDefinedIntOrString
+{
+    /**
+     * @var array<string|int, bool>
+     */
+    private array $shownTodos = [
+        0 => false,
+        'fallback_todo' => true,
+    ];
+
+    public function run(string|int $index): void
+    {
+  		if (! array_key_exists($index, $this->shownTodos)) {
+            return;
+        }
+
+        $this->shownTodos[$index] = true;
+    }
+}
diff --git a/rules/Php85/Rector/FuncCall/ArrayKeyExistsNullToEmptyStringRector.php b/rules/Php85/Rector/FuncCall/ArrayKeyExistsNullToEmptyStringRector.php
index 9618aa6afed..f2f074fd338 100644
--- a/rules/Php85/Rector/FuncCall/ArrayKeyExistsNullToEmptyStringRector.php
+++ b/rules/Php85/Rector/FuncCall/ArrayKeyExistsNullToEmptyStringRector.php
@@ -4,6 +4,8 @@
 
 namespace Rector\Php85\Rector\FuncCall;
 
+use PHPStan\Type\UnionType;
+use PHPStan\Type\TypeCombinator;
 use PhpParser\Node;
 use PhpParser\Node\Expr\FuncCall;
 use PHPStan\Analyser\Scope;
@@ -88,12 +90,21 @@ public function refactor(Node $node): ?Node
             return null;
         }
 
-        $parametersAcceptor = ParametersAcceptorSelectorVariantsWrapper::select($functionReflection, $node, $scope);
+        $argPosition = $this->argsAnalyzer->resolveArgPosition($args, 'key', 0);
+        $originalType = $this->getType($args[$argPosition]->value);
+
+        if ($originalType instanceof UnionType) {
+            $withoutNullParameterType = TypeCombinator::removeNull($originalType);
+            if ($withoutNullParameterType->equals($originalType)) {
+                return null;
+            }
+        }
 
+        $parametersAcceptor = ParametersAcceptorSelectorVariantsWrapper::select($functionReflection, $node, $scope);
         $result = $this->nullToStrictStringIntConverter->convertIfNull(
             $node,
             $args,
-            $this->argsAnalyzer->resolveArgPosition($args, 'key', 0),
+            $argPosition,
             $isTrait,
             $scope,
             $parametersAcceptor