diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index 340c83aff9..c9064a4a36 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -53,6 +53,7 @@
 <ol>
 	<li><a href="#changelog">Changelog</a>
 	<ol style="list-style-type: lower-roman;">
+		<li><a href="#v30rc8">Changes since RC-8</a></li>
 		<li><a href="#v30rc7">Changes since RC-7</a></li>
 		<li><a href="#v30rc6">Changes since RC-6</a></li>
 		<li><a href="#v30rc5">Changes since RC-5</a></li>
@@ -79,7 +80,13 @@
 
 		<div class="content">
 
-	<a name="v30rc7"></a><h3>1.i. Changes since 3.0.RC7</h3>
+	<a name="v30rc8"></a><h3>1.i. Changes since 3.0.RC8</h3>
+
+	<ul>
+		<li>[Fix] Cleaned usernames contain only single spaces, so "a_name" and "a__name" are treated as the same name (Bug #15634)</li>
+	</ul>
+
+	<a name="v30rc7"></a><h3>1.ii. Changes since 3.0.RC7</h3>
 
 	<ul>
 		<li>[Fix] Fixed MSSQL related bug in the update system</li>
@@ -114,7 +121,7 @@
 		<li>[Fix] No duplication of active topics (Bug #15474)</li>
 	</ul>
 
-	<a name="v30rc6"></a><h3>1.ii. Changes since 3.0.RC6</h3>
+	<a name="v30rc6"></a><h3>1.iii. Changes since 3.0.RC6</h3>
 
 	<ul>
 		<li>[Fix] Submitting language changes using acp_language (Bug #14736)</li>
@@ -124,7 +131,7 @@
 		<li>[Fix] Able to request new password (Bug #14743)</li>
 	</ul>
 
-	<a name="v30rc5"></a><h3>1.iii. Changes since 3.0.RC5</h3>
+	<a name="v30rc5"></a><h3>1.iv. Changes since 3.0.RC5</h3>
 
 	<ul>
 		<li>[Feature] Removing constant PHPBB_EMBEDDED in favor of using an exit_handler(); the constant was meant to achive this more or less.</li>
@@ -187,7 +194,7 @@
 		<li>[Sec] New password hashing mechanism for storing passwords (#i42)</li>
 	</ul>
 
-	<a name="v30rc4"></a><h3>1.iv. Changes since 3.0.RC4</h3>
+	<a name="v30rc4"></a><h3>1.v. Changes since 3.0.RC4</h3>
 
 	<ul>
 		<li>[Fix] MySQL, PostgreSQL and SQLite related database fixes (Bug #13862)</li>
@@ -238,7 +245,7 @@
 		<li>[Fix] odbc_autocommit causing existing result sets to be dropped (Bug #14182)</li>
 	</ul>
 
-	<a name="v30rc3"></a><h3>1.v. Changes since 3.0.RC3</h3>
+	<a name="v30rc3"></a><h3>1.vi. Changes since 3.0.RC3</h3>
 
 	<ul>
 		<li>[Fix] Fixing some subsilver2 and prosilver style issues</li>
@@ -347,7 +354,7 @@
 
 	</ul>
 
-	<a name="v30rc2"></a><h3>1.vi. Changes since 3.0.RC2</h3>
+	<a name="v30rc2"></a><h3>1.vii. Changes since 3.0.RC2</h3>
 
 	<ul>
 		<li>[Fix] Re-allow searching within the memberlist</li>
@@ -393,7 +400,7 @@
 
 	</ul>
 
-	<a name="v30rc1"></a><h3>1.vii. Changes since 3.0.RC1</h3>
+	<a name="v30rc1"></a><h3>1.viii. Changes since 3.0.RC1</h3>
 
 	<ul>
 		<li>[Fix] (X)HTML issues within the templates (Bug #11255, #11255)</li>
diff --git a/phpBB/includes/utf/utf_tools.php b/phpBB/includes/utf/utf_tools.php
index e7f144af51..b30f28aac9 100644
--- a/phpBB/includes/utf/utf_tools.php
+++ b/phpBB/includes/utf/utf_tools.php
@@ -1829,6 +1829,9 @@ function utf8_clean_string($text)
 	// Other control characters
 	$text = preg_replace('#(?:[\x00-\x1F\x7F]+|(?:\xC2[\x80-\x9F])+)#', '', $text);
 
+	// we need to reduce multiple spaces to a single one
+	$text = preg_replace('# {2,}#', ' ', $text);
+
 	// we can use trim here as all the other space characters should have been turned
 	// into normal ASCII spaces by now
 	return trim($text);
diff --git a/phpBB/install/database_update.php b/phpBB/install/database_update.php
index 0145c2746a..b3be23858d 100644
--- a/phpBB/install/database_update.php
+++ b/phpBB/install/database_update.php
@@ -571,7 +571,7 @@ else
 
 // Checks/Operations that have to be completed prior to starting the update itself
 $exit = false;
-if (version_compare($current_version, '3.0.RC4', '<='))
+if (version_compare($current_version, '3.0.RC8', '<='))
 {
 	// Define missing language entries...
 	if (!isset($lang['CLEANING_USERNAMES']))
@@ -715,9 +715,13 @@ if (version_compare($current_version, '3.0.RC4', '<='))
 	// duplicates might be created. Since the column has to be unique such usernames
 	// must not exist. We need identify them and let the admin decide what to do
 	// about them.
+	// After RC8 this was changed again, but this time only usernames containing spaces
+	// are affected.
+	$sql_where = (version_compare($current_version, '3.0.RC4', '<=')) ? '' : "WHERE username_clean LIKE '% %'";
 	$sql = 'SELECT user_id, username, username_clean
-		FROM ' . USERS_TABLE . '
-		ORDER BY user_id ASC';
+		FROM ' . USERS_TABLE . "
+		$sql_where
+		ORDER BY user_id ASC";
 	$result = $db->sql_query($sql);
 
 	$colliding_users = $found_names = array();
@@ -2765,6 +2769,8 @@ function utf8_new_clean_string($text)
 	// Other control characters
 	$text = preg_replace('#(?:[\x00-\x1F\x7F]+|(?:\xC2[\x80-\x9F])+)#', '', $text);
 
+	$text = preg_replace('# {2,}#', ' ', $text);
+
 	// we can use trim here as all the other space characters should have been turned
 	// into normal ASCII spaces by now
 	return trim($text);