diff --git a/spec/Locator/ChangedFilesSpec.php b/spec/Locator/ChangedFilesSpec.php
index 88d8ed7f2..ec796be2d 100644
--- a/spec/Locator/ChangedFilesSpec.php
+++ b/spec/Locator/ChangedFilesSpec.php
@@ -60,7 +60,7 @@ function it_will_list_all_diffed_files(GitRepository $repository, Filesystem $fi
         $result->shouldBeAnInstanceOf(FilesCollection::class);
         $result[0]->getPathname()->shouldBe('file1.txt');
         $result[1]->getPathname()->shouldBe('file2.txt');
-        $result->getIterator()->count()->shouldBe(2);
+        $result->shouldHaveCount(2);
     }
 
     function it_will_not_list_non_existing_files(GitRepository $repository, Filesystem $filesystem, Diff $diff, WorkingCopy $workingCopy)
@@ -74,7 +74,7 @@ function it_will_not_list_non_existing_files(GitRepository $repository, Filesyst
 
         $result = $this->locateFromGitRepository();
         $result->shouldBeAnInstanceOf(FilesCollection::class);
-        $result->getIterator()->count()->shouldBe(0);
+        $result->shouldHaveCount(0);
     }
 
     function it_will_list_all_diffed_files_from_raw_diff_input(GitRepository $repository, Filesystem $filesystem)
@@ -96,6 +96,6 @@ function it_will_list_all_diffed_files_from_raw_diff_input(GitRepository $reposi
         $result = $this->locateFromRawDiffInput($rawDiff);
         $result->shouldBeAnInstanceOf(FilesCollection::class);
         $result[0]->getPathname()->shouldBe('file.txt');
-        $result->getIterator()->count()->shouldBe(1);
+        $result->shouldHaveCount(1);
     }
 }
diff --git a/spec/Locator/ListedFilesSpec.php b/spec/Locator/ListedFilesSpec.php
index 728029ca6..34348db6d 100644
--- a/spec/Locator/ListedFilesSpec.php
+++ b/spec/Locator/ListedFilesSpec.php
@@ -32,6 +32,6 @@ function it_will_list_all_listed_files()
         $result->shouldBeAnInstanceOf(FilesCollection::class);
         $result[0]->getPathname()->shouldBe('file1.txt');
         $result[1]->getPathname()->shouldBe('file2.txt');
-        $result->getIterator()->count()->shouldBe(2);
+        $result->shouldHaveCount(2);
     }
 }
diff --git a/src/Collection/FilesCollection.php b/src/Collection/FilesCollection.php
index 20aa29d45..d96bc7c8d 100644
--- a/src/Collection/FilesCollection.php
+++ b/src/Collection/FilesCollection.php
@@ -213,12 +213,21 @@ public function filterByFileList(Traversable $fileList): FilesCollection
 
     public function ensureFiles(self $files): FilesCollection
     {
-        $newFiles = new self($this->toArray());
+        $newFiles = new self();
+        $knownPaths = [];
+
+        foreach (parent::getIterator() as $value) {
+            $newFiles->add($value);
+            $knownPaths[$value->getPathname()] = true;
+        }
 
         foreach ($files as $file) {
-            if (!$newFiles->contains($file)) {
-                $newFiles->add($file);
+            $path = $file->getPathname();
+            if (isset($knownPaths[$path])) {
+                continue;
             }
+            $newFiles->add($file);
+            $knownPaths[$path] = true;
         }
 
         return $newFiles;
@@ -234,14 +243,28 @@ public function ignoreSymlinks(): FilesCollection
     /**
      * SplFileInfo cannot be serialized. Therefor, we help PHP a bit.
      * This stuff is used for running tasks in parallel.
+     *
+     * @psalm-suppress DocblockTypeContradiction
+     * @psalm-suppress RedundantConditionGivenDocblockType
      */
     public function __serialize(): array
     {
-        return $this->map(function (SplFileInfo $fileInfo): string {
-            return $fileInfo instanceof SymfonySplFileInfo
-                ? $fileInfo->getRelativePathname()
-                : $fileInfo->getPathname();
-        })->toArray();
+        $paths = [];
+        foreach (parent::getIterator() as $value) {
+            if (\is_string($value)) {
+                $paths[] = $value;
+                continue;
+            }
+            if ($value instanceof SymfonySplFileInfo) {
+                $paths[] = $value->getRelativePathname();
+                continue;
+            }
+            if ($value instanceof SplFileInfo) {
+                $paths[] = $value->getPathname();
+            }
+        }
+
+        return $paths;
     }
 
     /**
@@ -250,25 +273,57 @@ public function __serialize(): array
      */
     public function __unserialize(array $data): void
     {
-        $files = $data;
         $this->clear();
-        foreach ($files as $file) {
-            $this->add(new SymfonySplFileInfo($file, dirname($file), $file));
+        foreach ($data as $path) {
+            $this->add($path);
         }
     }
 
     /**
-     * Help Psalm out a bit:
-     *
-     * @return \ArrayIterator<array-key, SplFileInfo>
+     * @return \Generator<array-key, SplFileInfo>
      */
-    public function getIterator(): \ArrayIterator
+    public function getIterator(): \Generator
     {
-        return new \ArrayIterator($this->toArray());
+        foreach (parent::getIterator() as $key => $value) {
+            yield $key => $this->hydrateFileInfo($value);
+        }
     }
 
     public function toFileList(): string
     {
-        return \implode(PHP_EOL, $this->toArray());
+        $lines = [];
+        foreach ($this as $file) {
+            $lines[] = $file->getPathname();
+        }
+
+        return \implode(PHP_EOL, $lines);
+    }
+
+    /**
+     * @return SplFileInfo|false
+     */
+    public function first()
+    {
+        $value = parent::first();
+
+        return $value === false ? false : $this->hydrateFileInfo($value);
+    }
+
+    /**
+     * @param mixed $value
+     */
+    private function hydrateFileInfo($value): SplFileInfo
+    {
+        if ($value instanceof SplFileInfo) {
+            return $value;
+        }
+
+        if (\is_string($value)) {
+            return new SymfonySplFileInfo($value, \dirname($value), $value);
+        }
+
+        throw new \LogicException(
+            'Unexpected element type in FilesCollection: ' . get_debug_type($value)
+        );
     }
 }
diff --git a/src/Console/Command/Git/CommitMsgCommand.php b/src/Console/Command/Git/CommitMsgCommand.php
index 1f907fa82..77ac86745 100644
--- a/src/Console/Command/Git/CommitMsgCommand.php
+++ b/src/Console/Command/Git/CommitMsgCommand.php
@@ -119,6 +119,16 @@ public function execute(InputInterface $input, OutputInterface $output): int
 
         $results = $this->taskRunner->run($context);
 
+        if ($this->io->isVerbose()) {
+            $this->io->write([
+                PHP_EOL,
+                sprintf(
+                    '<comment>Peak memory usage: %.1f MB</comment>',
+                    (float) memory_get_peak_usage(true) / 1024.0 / 1024.0
+                )
+            ]);
+        }
+
         return $results->isFailed() ? self::EXIT_CODE_NOK : self::EXIT_CODE_OK;
     }
 
diff --git a/src/Console/Command/Git/PreCommitCommand.php b/src/Console/Command/Git/PreCommitCommand.php
index 2e00bba15..e0e5143e3 100644
--- a/src/Console/Command/Git/PreCommitCommand.php
+++ b/src/Console/Command/Git/PreCommitCommand.php
@@ -90,6 +90,16 @@ public function execute(InputInterface $input, OutputInterface $output): int
 
         $results = $this->taskRunner->run($context);
 
+        if ($this->io->isVerbose()) {
+            $this->io->write([
+                PHP_EOL,
+                sprintf(
+                    '<comment>Peak memory usage: %.1f MB</comment>',
+                    (float) memory_get_peak_usage(true) / 1024.0 / 1024.0
+                )
+            ]);
+        }
+
         return $results->isFailed() ? self::EXIT_CODE_NOK : self::EXIT_CODE_OK;
     }
 
diff --git a/src/Console/Command/RunCommand.php b/src/Console/Command/RunCommand.php
index e65ade451..03118d012 100644
--- a/src/Console/Command/RunCommand.php
+++ b/src/Console/Command/RunCommand.php
@@ -102,6 +102,16 @@ public function execute(InputInterface $input, OutputInterface $output): int
 
         $results = $this->taskRunner->run($context);
 
+        if ($this->io->isVerbose()) {
+            $this->io->write([
+                PHP_EOL,
+                sprintf(
+                    '<comment>Peak memory usage: %.1f MB</comment>',
+                    (float) memory_get_peak_usage(true) / 1024.0 / 1024.0
+                )
+            ]);
+        }
+
         return $results->isFailed() ? self::EXIT_CODE_NOK : self::EXIT_CODE_OK;
     }