diff --git a/lib/private/Files/ObjectStore/ObjectStoreStorage.php b/lib/private/Files/ObjectStore/ObjectStoreStorage.php
index 58359787f5769..4fa62747d1acb 100644
--- a/lib/private/Files/ObjectStore/ObjectStoreStorage.php
+++ b/lib/private/Files/ObjectStore/ObjectStoreStorage.php
@@ -304,8 +304,9 @@ public function filetype(string $path): string|false {
 	public function fopen(string $path, string $mode) {
 		$path = $this->normalizePath($path);
 
-		if (strrpos($path, '.') !== false) {
-			$ext = substr($path, strrpos($path, '.'));
+		$baseName = basename($path);
+		if (strrpos($baseName, '.') !== false) {
+			$ext = substr($baseName, strrpos($baseName, '.'));
 		} else {
 			$ext = '';
 		}
@@ -366,6 +367,9 @@ public function fopen(string $path, string $mode) {
 				}
 
 				$tmpFile = Server::get(ITempManager::class)->getTemporaryFile($ext);
+				if ($tmpFile === false) {
+					return false;
+				}
 				$handle = fopen($tmpFile, $mode);
 				return CallbackWrapper::wrap($handle, null, null, function () use ($path, $tmpFile): void {
 					$this->writeBack($tmpFile, $path);
@@ -380,6 +384,9 @@ public function fopen(string $path, string $mode) {
 			case 'c':
 			case 'c+':
 				$tmpFile = Server::get(ITempManager::class)->getTemporaryFile($ext);
+				if ($tmpFile === false) {
+					return false;
+				}
 				if ($this->file_exists($path)) {
 					$source = $this->fopen($path, 'r');
 					file_put_contents($tmpFile, $source);
diff --git a/tests/lib/Files/ObjectStore/ObjectStoreStorageTest.php b/tests/lib/Files/ObjectStore/ObjectStoreStorageTest.php
index c896eb377978c..74143d8d057e8 100644
--- a/tests/lib/Files/ObjectStore/ObjectStoreStorageTest.php
+++ b/tests/lib/Files/ObjectStore/ObjectStoreStorageTest.php
@@ -261,4 +261,19 @@ public function testCopyFolderSize(): void {
 
 		$this->assertEquals(3, $cache->get('target')->getSize());
 	}
+
+	public function testFopenWriteInDottedDirectoryWithoutExtension(): void {
+		$dir = '0. Folder.With.Dots/Subfolder';
+		$this->instance->mkdir($dir);
+
+		$filePath = $dir . '/extensionlessfile';
+		$handle = $this->instance->fopen($filePath, 'w');
+		$this->assertIsResource($handle);
+
+		fwrite($handle, 'sample content');
+		fclose($handle);
+
+		$this->assertTrue($this->instance->file_exists($filePath));
+		$this->assertEquals('sample content', $this->instance->file_get_contents($filePath));
+	}
 }