diff --git a/other/upgrade.php b/other/upgrade.php
index 2dc4bccb62..b91cfd25bf 100644
--- a/other/upgrade.php
+++ b/other/upgrade.php
@@ -3445,31 +3445,6 @@ function ConvertUtf8()
 		require_once($sourcedir . '/Subs-Admin.php');
 		updateSettingsFile(array('db_character_set' => 'utf8'));
 
-		// The conversion might have messed up some serialized strings. Fix them!
-		$request = $smcFunc['db_query']('', '
-			SELECT id_action, extra
-			FROM {db_prefix}log_actions
-			WHERE action IN ({string:remove}, {string:delete})',
-			array(
-				'remove' => 'remove',
-				'delete' => 'delete',
-			)
-		);
-		while ($row = $smcFunc['db_fetch_assoc']($request))
-		{
-			if (@safe_unserialize($row['extra']) === false && preg_match('~^(a:3:{s:5:"topic";i:\d+;s:7:"subject";s:)(\d+):"(.+)"(;s:6:"member";s:5:"\d+";})$~', $row['extra'], $matches) === 1)
-				$smcFunc['db_query']('', '
-					UPDATE {db_prefix}log_actions
-					SET extra = {string:extra}
-					WHERE id_action = {int:current_action}',
-					array(
-						'current_action' => $row['id_action'],
-						'extra' => $matches[1] . strlen($matches[3]) . ':"' . $matches[3] . '"' . $matches[4],
-					)
-				);
-		}
-		$smcFunc['db_free_result']($request);
-
 		if ($upcontext['dropping_index'] && $command_line)
 		{
 			echo "\n" . '', $txt['upgrade_fulltext_error'], '';
@@ -3510,22 +3485,27 @@ function upgrade_unserialize($string)
 		$data = @safe_unserialize($string);
 
 		// The serialized data is broken.
-		if ($data === false)
+		// OR... Has strings that are not utf8.
+		if (($data === false) || (mb_check_encoding($string, 'UTF-8') === false))
 		{
 			// This bit fixes incorrect string lengths, which can happen if the character encoding was changed (e.g. conversion to UTF-8)
 			$new_string = preg_replace_callback(
 				'~\bs:(\d+):"(.*?)";(?=$|[bidsaO]:|[{}}]|N;)~s',
 				function ($matches)
 				{
+					// If not utf8, use cheezy-21-encoding, because json_encode ONLY works on utf8
+					// Will decode this after json_encode; utf8 conversion can then proceed properly on the non-utf8 data
+					if (mb_check_encoding($matches[2], 'UTF-8') === false)
+					{
+						$matches[2] = 'czy21enc:' . bin2hex($matches[2]);
+					}
 					return 's:' . strlen($matches[2]) . ':"' . $matches[2] . '";';
 				},
 				$string
 			);
 
-			// @todo Add more possible fixes here. For example, fix incorrect array lengths, try to handle truncated strings gracefully, etc.
-
 			// Did it work?
-			$data = @safe_unserialize($string);
+			$data = @safe_unserialize($new_string);
 		}
 	}
 	// Just a plain string, then.
@@ -3648,7 +3628,23 @@ function serialize_to_json()
 						if (!$temp && $command_line)
 							echo "\n - Failed to unserialize the '" . $var . "' setting. Skipping.";
 						elseif ($temp !== false)
-							$new_settings[$var] = json_encode($temp);
+						{
+							$new_settings[$var] = json_encode($temp, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
+							if ($new_settings[$var] === false)
+								$new_settings[$var] = '';
+							else
+							{
+								// Decode cheezy-21-encoding to preserve non-utf8 strings before utf8 conversion
+								$new_settings[$var] = preg_replace_callback(
+									'~"czy21enc:((?:[0-9a-f]{2})*)"~',
+									function ($matches)
+									{
+										return '"' . hex2bin($matches[1]) . '"';
+									},
+									$new_settings[$var]
+								);
+							}
+						}
 					}
 				}
 
@@ -3685,7 +3681,21 @@ function serialize_to_json()
 
 						if ($temp !== false)
 						{
-							$row['value'] = json_encode($temp);
+							$row['value'] = json_encode($temp, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
+							if ($row['value'] === false)
+								$row['value'] = '';
+							else
+							{
+								// Decode cheezy-21-encoding to preserve non-utf8 strings before utf8 conversion
+								$row['value'] = preg_replace_callback(
+									'~"czy21enc:((?:[0-9a-f]{2})*)"~',
+									function ($matches)
+									{
+										return '"' . hex2bin($matches[1]) . '"';
+									},
+									$row['value']
+								);
+							}
 
 							// Even though we have all values from the table, UPDATE is still faster than REPLACE
 							$smcFunc['db_query']('', '
@@ -3761,7 +3771,21 @@ function serialize_to_json()
 										echo "\nFailed to unserialize " . $row[$col] . ". Setting to empty value.\n";
 								}
 
-								$row[$col] = json_encode($temp);
+								$row[$col] = json_encode($temp, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
+								if ($row[$col] === false)
+									$row[$col] = '';
+								else
+								{
+									// Decode cheezy-21-encoding to preserve non-utf8 strings before utf8 conversion
+									$row[$col] = preg_replace_callback(
+										'~"czy21enc:((?:[0-9a-f]{2})*)"~',
+										function ($matches)
+										{
+											return '"' . hex2bin($matches[1]) . '"';
+										},
+										$row[$col]
+									);
+								}
 
 								// Build our SET string and variables array
 								$update .= (empty($update) ? '' : ', ') . $col . ' = {string:' . $col . '}';