diff --git a/src/_h5ai/server/php/inc/Archive.php b/src/_h5ai/server/php/inc/Archive.php
index 2068775e..1a73abbc 100644
--- a/src/_h5ai/server/php/inc/Archive.php
+++ b/src/_h5ai/server/php/inc/Archive.php
@@ -57,7 +57,7 @@ class Archive {
 		try {
 
 			if ($format === "tar") {
-				$cmd = Archive::$TAR_PASSTHRU_CMD;
+				return $this->create_tar();
 			} else if ($format === "zip") {
 				$cmd = Archive::$ZIP_PASSTHRU_CMD;
 			} else {
@@ -77,6 +77,54 @@ class Archive {
 	}
 
 
+	private function create_tar() {
+
+		// POSIX.1-1988 UStar implementation, by @TvdW
+
+		$root_path = $this->app->get_root_abs_path();
+
+		foreach (array_values($this->files) as $file) {
+
+			// TAR supports filenames up to 253 chars, but the name should be split ubti a 154-byte prefix and 99-byte name
+			assert(substr($file, 0, strlen($root_path)) == $root_path);
+			$local_filename = normalize_path(substr($file, strlen($root_path) + 1));
+			$filename_parts = array('', substr($local_filename, -99));
+			if (strlen($local_filename) > 99) $filename_parts[0] = substr($local_filename, 0, -99);
+			if (strlen($filename_parts[0]) > 154) $filename_parts[0] = substr($filename_parts[0], -154);
+
+			$size = filesize($file);
+
+			$file_header = 
+				 str_pad($filename_parts[1], 100, "\0") // first filename part
+				."0000755\0"."0000000\0"."0000000\0" // File mode and uid/gid
+				.str_pad(decoct($size), 11, "0", STR_PAD_LEFT)."\0" // File size
+				.str_pad(decoct(time()), 11, "0", STR_PAD_LEFT)."\0" // Modification time
+				."        " // checksum (filled in later)
+				."0" // file type
+				.str_repeat("\0", 100)
+				."ustar 00"
+				.str_repeat("\0", 92)
+				.str_pad($filename_parts[0], 155, "\0");
+			assert(strlen($file_header) == 512);
+
+			// Checksum
+			$checksum = array_sum(array_map('ord', str_split($file_header)));
+			$checksum = str_pad(decoct($checksum), 6, "0", STR_PAD_LEFT)."\0 ";
+			$file_header = substr_replace($file_header, $checksum, 148, 8);
+
+			echo $file_header;
+			readfile($file);
+
+			$pad_file = 512 - ($size % 512);
+			if ($pad_file) echo str_repeat("\0", $pad_file);
+
+		}
+
+		return 0;
+
+	}
+
+
 	private function add_hrefs($hrefs) {
 
 		foreach ($hrefs as $href) {
@@ -132,4 +180,4 @@ class Archive {
 	}
 }
 
-?>
\ No newline at end of file
+?>