diff --git a/lib/private/Files/ObjectStore/S3ObjectTrait.php b/lib/private/Files/ObjectStore/S3ObjectTrait.php
index 8fa6d67faa3cd..c50218a01a482 100644
--- a/lib/private/Files/ObjectStore/S3ObjectTrait.php
+++ b/lib/private/Files/ObjectStore/S3ObjectTrait.php
@@ -154,16 +154,24 @@ protected function writeMultiPart(string $urn, StreamInterface $stream, string $
 	public function writeObject($urn, $stream, string $mimetype = null) {
 		$psrStream = Utils::streamFor($stream);
 
-		// ($psrStream->isSeekable() && $psrStream->getSize() !== null) evaluates to true for a On-Seekable stream
-		// so the optimisation does not apply
-		$buffer = new Psr7\Stream(fopen("php://memory", 'rwb+'));
-		Utils::copyToStream($psrStream, $buffer, $this->putSizeLimit);
-		$buffer->seek(0);
-		if ($buffer->getSize() < $this->putSizeLimit) {
+		$streamSize = $psrStream->getSize();
+		if ($psrStream->isSeekable() && (int)$streamSize !== 0) {
+			$loadStream = $psrStream;
+		} else {
+			// For cases where the stream reports seekable but no size is returned
+			$buffer = new Psr7\Stream(fopen("php://temp", 'rwb+'));
+			Utils::copyToStream($psrStream, $buffer, $this->putSizeLimit);
+			$buffer->seek(0);
+			$streamSize = $buffer->getSize();
+			$loadStream = $streamSize < $this->putSizeLimit
+				? $buffer
+				: new Psr7\AppendStream([$buffer, $psrStream]);
+		}
+
+		if ($streamSize < $this->putSizeLimit) {
 			// buffer is fully seekable, so use it directly for the small upload
-			$this->writeSingle($urn, $buffer, $mimetype);
+			$this->writeSingle($urn, $loadStream, $mimetype);
 		} else {
-			$loadStream = new Psr7\AppendStream([$buffer, $psrStream]);
 			$this->writeMultiPart($urn, $loadStream, $mimetype);
 		}
 	}
diff --git a/lib/private/Files/Stream/SeekableHttpStream.php b/lib/private/Files/Stream/SeekableHttpStream.php
index 51ccaeba998cb..ef930cef9000b 100644
--- a/lib/private/Files/Stream/SeekableHttpStream.php
+++ b/lib/private/Files/Stream/SeekableHttpStream.php
@@ -219,6 +219,7 @@ public function stream_tell() {
 	public function stream_stat() {
 		if ($this->getCurrent()) {
 			$stat = fstat($this->getCurrent());
+			$stat = $stat ? $stat : [];
 			$stat['size'] = $this->totalSize;
 			return $stat;
 		} else {
diff --git a/tests/lib/Files/ObjectStore/S3Test.php b/tests/lib/Files/ObjectStore/S3Test.php
index fd451dc3c016f..e1212ab89d104 100644
--- a/tests/lib/Files/ObjectStore/S3Test.php
+++ b/tests/lib/Files/ObjectStore/S3Test.php
@@ -80,7 +80,15 @@ public function testUploadNonSeekable() {
 
 		$s3 = $this->getInstance();
 
-		$s3->writeObject('multiparttest', NonSeekableStream::wrap(fopen(__FILE__, 'r')));
+		// We need an actual non-seekable resource here as NonSeekableStream won't be enough
+		// when it is passed to the GuzzleHttp\Psr7\Utils::streamFor
+		// which checks the actual stream meta data using stream_get_meta_data
+		@posix_mkfifo('/tmp/fifo', 0644);
+		$stream = fopen('/tmp/fifo', 'rw+');
+		stream_set_blocking($stream, false);
+		fwrite($stream, file_get_contents(__FILE__));
+
+		$s3->writeObject('multiparttest', NonSeekableStream::wrap($stream));
 
 		$result = $s3->readObject('multiparttest');
 
@@ -119,7 +127,7 @@ public function testEmptyUpload() {
 		$s3 = $this->getInstance();
 
 		$emptyStream = fopen("php://memory", "r");
-		fwrite($emptyStream, null);
+		fwrite($emptyStream, '');
 
 		$s3->writeObject('emptystream', $emptyStream);