diff --git a/core/includes/common.inc b/core/includes/common.inc
index 49cf6e104a72aafac9435f9aaf721716d9ab9634..23cecc8c778f6e9574be3d73ac08e7798fb8a5d9 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -251,42 +251,46 @@ function check_url($uri) {
  *   A translated string representation of the size.
  */
 function format_size($size, $langcode = NULL) {
-  if ($size < Bytes::KILOBYTE) {
+  $absolute_size = abs($size);
+  if ($absolute_size < Bytes::KILOBYTE) {
     return \Drupal::translation()->formatPlural($size, '1 byte', '@count bytes', [], ['langcode' => $langcode]);
   }
-  else {
-    // Convert bytes to kilobytes.
-    $size = $size / Bytes::KILOBYTE;
-    $units = ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
-    foreach ($units as $unit) {
-      if (round($size, 2) >= Bytes::KILOBYTE) {
-        $size = $size / Bytes::KILOBYTE;
-      }
-      else {
-        break;
-      }
-    }
-    $args = ['@size' => round($size, 2)];
-    $options = ['langcode' => $langcode];
-    switch ($unit) {
-      case 'KB':
-        return new TranslatableMarkup('@size KB', $args, $options);
-      case 'MB':
-        return new TranslatableMarkup('@size MB', $args, $options);
-      case 'GB':
-        return new TranslatableMarkup('@size GB', $args, $options);
-      case 'TB':
-        return new TranslatableMarkup('@size TB', $args, $options);
-      case 'PB':
-        return new TranslatableMarkup('@size PB', $args, $options);
-      case 'EB':
-        return new TranslatableMarkup('@size EB', $args, $options);
-      case 'ZB':
-        return new TranslatableMarkup('@size ZB', $args, $options);
-      case 'YB':
-        return new TranslatableMarkup('@size YB', $args, $options);
+  // Create a multiplier to preserve the sign of $size.
+  $sign = $absolute_size / $size;
+  foreach (['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'] as $unit) {
+    $absolute_size /= Bytes::KILOBYTE;
+    $rounded_size = round($absolute_size, 2);
+    if ($rounded_size < Bytes::KILOBYTE) {
+      break;
     }
   }
+  $args = ['@size' => $rounded_size * $sign];
+  $options = ['langcode' => $langcode];
+  switch ($unit) {
+    case 'KB':
+      return new TranslatableMarkup('@size KB', $args, $options);
+
+    case 'MB':
+      return new TranslatableMarkup('@size MB', $args, $options);
+
+    case 'GB':
+      return new TranslatableMarkup('@size GB', $args, $options);
+
+    case 'TB':
+      return new TranslatableMarkup('@size TB', $args, $options);
+
+    case 'PB':
+      return new TranslatableMarkup('@size PB', $args, $options);
+
+    case 'EB':
+      return new TranslatableMarkup('@size EB', $args, $options);
+
+    case 'ZB':
+      return new TranslatableMarkup('@size ZB', $args, $options);
+
+    case 'YB':
+      return new TranslatableMarkup('@size YB', $args, $options);
+  }
 }
 
 /**
diff --git a/core/tests/Drupal/KernelTests/Core/Common/SizeTest.php b/core/tests/Drupal/KernelTests/Core/Common/SizeTest.php
index 82ff53086ba3a006c40fc874fccb3f352c629331..f595cfcab5ec8dbfa2bf5aed11099fe62acae4ab 100644
--- a/core/tests/Drupal/KernelTests/Core/Common/SizeTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Common/SizeTest.php
@@ -29,8 +29,12 @@ public function testCommonFormatSize($expected, $input) {
   public function providerTestCommonFormatSize() {
     $kb = Bytes::KILOBYTE;
     return [
+      ['0 bytes', 0],
       ['1 byte', 1],
+      ['-1 bytes', -1],
       ['2 bytes', 2],
+      ['-2 bytes', -2],
+      ['1023 bytes', $kb - 1],
       ['1 KB', $kb],
       ['1 MB', pow($kb, 2)],
       ['1 GB', pow($kb, 3)],
@@ -39,10 +43,13 @@ public function providerTestCommonFormatSize() {
       ['1 EB', pow($kb, 6)],
       ['1 ZB', pow($kb, 7)],
       ['1 YB', pow($kb, 8)],
-      // Rounded to 1 MB - not 1000 or 1024 kilobyte
+      ['1024 YB', pow($kb, 9)],
+      // Rounded to 1 MB - not 1000 or 1024 kilobytes
       ['1 MB', ($kb * $kb) - 1],
+      ['-1 MB', -(($kb * $kb) - 1)],
       // Decimal Megabytes
       ['3.46 MB', 3623651],
+      ['3.77 GB', 4053371676],
       // Decimal Petabytes
       ['59.72 PB', 67234178751368124],
       // Decimal Yottabytes