diff --git a/bench/rename_class_const_fetch_lookup_bench.php b/bench/rename_class_const_fetch_lookup_bench.php
new file mode 100644
index 00000000000..7e51e783eee
--- /dev/null
+++ b/bench/rename_class_const_fetch_lookup_bench.php
@@ -0,0 +1,100 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Benchmark for RenameClassRector::shouldSkipClassConstFetchForMissingConstantName().
+ *
+ * For every fully-qualified class-const fetch node the guard used to scan the whole configured
+ * rename map, running isName() on each entry to find the one matching the node. Upgrade sets
+ * configure thousands of class renames, so this is a per-node linear scan.
+ *
+ * The change looks the node name up in the map directly (the map is keyed by old class, and a
+ * node has a single name), the same hash lookup the rename itself already uses.
+ *
+ * This bench drives refactor() over many real class-const fetches (\DateTime::ATOM) that are NOT
+ * in the rename map - the worst case, where the old code scans every entry before giving up.
+ *
+ * Run on both branches to compare:
+ *   php bench/rename_class_const_fetch_lookup_bench.php
+ *
+ * Reports CPU time (user+sys) and wall time; CPU is the reliable metric, wall is noisy under
+ * concurrent load.
+ */
+
+use PhpParser\Node\Name\FullyQualified;
+use Rector\DependencyInjection\LazyContainerFactory;
+use Rector\PhpParser\Node\BetterNodeFinder;
+use Rector\Renaming\Rector\Name\RenameClassRector;
+use Rector\Testing\TestingParser\TestingParser;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+const RENAMES = 500; // configured class renames, none matching the node below
+const FETCHES = 150; // class-const fetches per pass
+const REPEAT = 200;  // outer repeats over the whole set
+
+$rectorConfig = (new LazyContainerFactory())->create();
+$rectorConfig->boot();
+
+/** @var TestingParser $testingParser */
+$testingParser = $rectorConfig->make(TestingParser::class);
+
+/** @var BetterNodeFinder $betterNodeFinder */
+$betterNodeFinder = $rectorConfig->make(BetterNodeFinder::class);
+
+$rector = $rectorConfig->make(RenameClassRector::class);
+
+$configuration = [];
+for ($i = 0; $i < RENAMES; ++$i) {
+    $configuration['Bench\\SomeOldClass' . $i] = 'Bench\\SomeNewClass' . $i;
+}
+
+$rector->configure($configuration);
+
+$source = "<?php\n\nnamespace Bench;\n\n";
+for ($i = 0; $i < FETCHES; ++$i) {
+    // real class + real constant, class-const fetch, deliberately absent from the rename map
+    $source .= "\$x{$i} = \\DateTime::ATOM;\n";
+}
+
+$sourceFilePath = tempnam(sys_get_temp_dir(), 'bench_') . '.php';
+file_put_contents($sourceFilePath, $source);
+
+$stmts = $testingParser->parseFileToDecoratedNodes($sourceFilePath);
+
+/** @var FullyQualified[] $fullyQualifieds */
+$fullyQualifieds = $betterNodeFinder->findInstanceOf($stmts, FullyQualified::class);
+
+$cpuSeconds = static function (): float {
+    $usage = getrusage();
+    return $usage['ru_utime.tv_sec'] + $usage['ru_utime.tv_usec'] / 1_000_000
+        + $usage['ru_stime.tv_sec'] + $usage['ru_stime.tv_usec'] / 1_000_000;
+};
+
+$run = static function () use ($rector, $fullyQualifieds): void {
+    foreach ($fullyQualifieds as $fullyQualified) {
+        $rector->refactor($fullyQualified);
+    }
+};
+
+// warm up autoloading/reflection caches once, excluded from timing
+$run();
+
+$wallStart = microtime(true);
+$cpuStart = $cpuSeconds();
+
+for ($repeat = 0; $repeat < REPEAT; ++$repeat) {
+    $run();
+}
+
+$cpu = $cpuSeconds() - $cpuStart;
+$wall = microtime(true) - $wallStart;
+
+@unlink($sourceFilePath);
+
+$totalCalls = REPEAT * count($fullyQualifieds);
+
+printf('renames: %d, fetches: %d, repeats: %d, refactor() calls: %d%s', RENAMES, count($fullyQualifieds), REPEAT, $totalCalls, PHP_EOL);
+printf('CPU:  %.4f s  (%.3f us/call)%s', $cpu, $cpu / $totalCalls * 1_000_000, PHP_EOL);
+printf('wall: %.4f s%s', $wall, PHP_EOL);
diff --git a/rules/Renaming/Rector/Name/RenameClassRector.php b/rules/Renaming/Rector/Name/RenameClassRector.php
index 12b25abec45..f373fe4cb87 100644
--- a/rules/Renaming/Rector/Name/RenameClassRector.php
+++ b/rules/Renaming/Rector/Name/RenameClassRector.php
@@ -139,7 +139,8 @@ private function shouldSkipClassConstFetchForMissingConstantName(
         FullyQualified $fullyQualified,
         array $oldToNewClasses
     ): bool {
-        if (! $this->reflectionProvider->hasClass($fullyQualified->toString())) {
+        $oldClass = $fullyQualified->toString();
+        if (! $this->reflectionProvider->hasClass($oldClass)) {
             return false;
         }
 
@@ -149,24 +150,20 @@ private function shouldSkipClassConstFetchForMissingConstantName(
             return false;
         }
 
-        foreach ($oldToNewClasses as $oldClass => $newClass) {
-            if (! $this->isName($fullyQualified, $oldClass)) {
-                continue;
-            }
-
-            if (! $this->reflectionProvider->hasClass($newClass)) {
-                continue;
-            }
-
-            $classReflection = $this->reflectionProvider->getClass($newClass);
-            $oldClassReflection = $this->reflectionProvider->getClass($oldClass);
+        // the node name is looked up directly, same as the rename itself does, instead of scanning the whole map
+        $newClass = $oldToNewClasses[$oldClass] ?? null;
+        if ($newClass === null) {
+            return false;
+        }
 
-            if ($oldClassReflection->hasConstant($constFetchName) && ! $classReflection->hasConstant($constFetchName)) {
-                // should be skipped as new class does not have access to the constant
-                return true;
-            }
+        if (! $this->reflectionProvider->hasClass($newClass)) {
+            return false;
         }
 
-        return false;
+        $classReflection = $this->reflectionProvider->getClass($newClass);
+        $oldClassReflection = $this->reflectionProvider->getClass($oldClass);
+
+        // should be skipped as new class does not have access to the constant
+        return $oldClassReflection->hasConstant($constFetchName) && ! $classReflection->hasConstant($constFetchName);
     }
 }