diff --git a/wp-admin/options-permalink.php b/wp-admin/options-permalink.php
index e4c7b83a4e..a423915a23 100644
--- a/wp-admin/options-permalink.php
+++ b/wp-admin/options-permalink.php
@@ -75,36 +75,33 @@ include('admin-header.php');
 $home_path = get_home_path();
 $iis7_permalinks = iis7_supports_permalinks();
 
+$prefix = '';
+if ( ! got_mod_rewrite() && ! $iis7_permalinks )
+	$prefix .= '/index.php';
+if ( is_multisite() && !is_subdomain_install() && is_main_site() )
+	$prefix .= '/blog';
+
 if ( isset($_POST['permalink_structure']) || isset($_POST['category_base']) ) {
 	check_admin_referer('update-permalink');
 
 	if ( isset( $_POST['permalink_structure'] ) ) {
 		$permalink_structure = $_POST['permalink_structure'];
-		if ( ! empty( $permalink_structure ) ) {
-			$permalink_structure = preg_replace( '#/+#', '/', '/' . str_replace( '#', '', $permalink_structure ) );
-			if ( is_multisite() && ! is_subdomain_install() && is_main_site() )
-				$permalink_structure = '/blog' . $permalink_structure;
-		}
+		if ( ! empty( $permalink_structure ) )
+			$permalink_structure = $prefix . preg_replace( '#/+#', '/', '/' . str_replace( '#', '', $permalink_structure ) );
 		$wp_rewrite->set_permalink_structure( $permalink_structure );
 	}
 
 	if ( isset( $_POST['category_base'] ) ) {
 		$category_base = $_POST['category_base'];
-		if (! empty( $category_base ) ) {
-			$category_base = preg_replace('#/+#', '/', '/' . str_replace( '#', '', $category_base ) );
-			if ( is_multisite() && ! is_subdomain_install() && is_main_site() )
-				$category_base = '/blog' . $category_base;
-		}
+		if ( ! empty( $category_base ) )
+			$category_base = $prefix . preg_replace('#/+#', '/', '/' . str_replace( '#', '', $category_base ) );
 		$wp_rewrite->set_category_base( $category_base );
 	}
 
 	if ( isset( $_POST['tag_base'] ) ) {
 		$tag_base = $_POST['tag_base'];
-		if ( ! empty( $tag_base ) ) {
-			$tag_base = preg_replace('#/+#', '/', '/' . str_replace( '#', '', $tag_base ) );
-			if ( is_multisite() && ! is_subdomain_install() && is_main_site() )
-				$tag_base = '/blog' . $tag_base;
-		}
+		if ( ! empty( $tag_base ) )
+			$tag_base = $prefix . preg_replace('#/+#', '/', '/' . str_replace( '#', '', $tag_base ) );
 		$wp_rewrite->set_tag_base( $tag_base );
 	}
 }
@@ -166,16 +163,20 @@ if ( ! is_multisite() ) {
   <p><?php _e('By default WordPress uses web <abbr title="Universal Resource Locator">URL</abbr>s which have question marks and lots of numbers in them, however WordPress offers you the ability to create a custom URL structure for your permalinks and archives. This can improve the aesthetics, usability, and forward-compatibility of your links. A <a href="http://codex.wordpress.org/Using_Permalinks">number of tags are available</a>, and here are some examples to get you started.'); ?></p>
 
 <?php
-$prefix = '';
-
 if ( ! got_mod_rewrite() && ! $iis7_permalinks )
-	$prefix = '/index.php';
+	$permalink_structure = preg_replace( '|^/?index\.php|', '', $permalink_structure );
+
+if ( is_multisite() && !is_subdomain_install() && is_main_site() ) {
+	$permalink_structure = preg_replace( '|^/?blog|', '', $permalink_structure );
+	$category_base = preg_replace( '|^/?blog|', '', $category_base );
+	$tag_base = preg_replace( '|^/?blog|', '', $tag_base );
+}
 
 $structures = array(
 	'',
-	$prefix . '/%year%/%monthnum%/%day%/%postname%/',
-	$prefix . '/%year%/%monthnum%/%postname%/',
-	$prefix . '/archives/%post_id%'
+	'/%year%/%monthnum%/%day%/%postname%/',
+	'/%year%/%monthnum%/%postname%/',
+	'/archives/%post_id%'
 	);
 ?>
 <h3><?php _e('Common settings'); ?></h3>
@@ -198,16 +199,12 @@ $structures = array(
 	</tr>
 	<tr>
 		<th>
-			<label><input name="selection" id="custom_selection" type="radio" value="custom" class="tog"
-			<?php if ( !in_array($permalink_structure, $structures) ) { ?>
-			checked="checked"
-			<?php } ?>
-			 />
+			<label><input name="selection" id="custom_selection" type="radio" value="custom" class="tog" <?php checked( !in_array($permalink_structure, $structures) ); ?> />
 			<?php _e('Custom Structure'); ?>
 			</label>
 		</th>
 		<td>
-			<?php if ( is_multisite() && !is_subdomain_install() && is_main_site() ) { echo "/blog"; $permalink_structure = preg_replace( "|^/?blog|", "", $permalink_structure ); }?>
+			<?php echo $prefix; ?>
 			<input name="permalink_structure" id="permalink_structure" type="text" value="<?php echo esc_attr($permalink_structure); ?>" class="regular-text code" />
 		</td>
 	</tr>
@@ -223,11 +220,11 @@ $structures = array(
 <table class="form-table">
 	<tr>
 		<th><label for="category_base"><?php /* translators: prefix for category permalinks */ _e('Category base'); ?></label></th>
-		<td><?php if ( is_multisite() && !is_subdomain_install() && is_main_site() ) { echo "/blog"; $category_base = preg_replace( "|^/?blog|", "", $category_base ); }?> <input name="category_base" id="category_base" type="text" value="<?php echo esc_attr( $category_base ); ?>" class="regular-text code" /></td>
+		<td><?php echo $prefix; ?> <input name="category_base" id="category_base" type="text" value="<?php echo esc_attr( $category_base ); ?>" class="regular-text code" /></td>
 	</tr>
 	<tr>
 		<th><label for="tag_base"><?php _e('Tag base'); ?></label></th>
-		<td><?php if ( is_multisite() && !is_subdomain_install() && is_main_site() ) { echo "/blog"; $tag_base = preg_replace( "|^/?blog|", "", $tag_base ); }?> <input name="tag_base" id="tag_base" type="text" value="<?php echo esc_attr($tag_base); ?>" class="regular-text code" /></td>
+		<td><?php echo $prefix; ?> <input name="tag_base" id="tag_base" type="text" value="<?php echo esc_attr($tag_base); ?>" class="regular-text code" /></td>
 	</tr>
 	<?php do_settings_fields('permalink', 'optional'); ?>
 </table>
@@ -239,7 +236,7 @@ $structures = array(
 </p>
   </form>
 <?php if ( !is_multisite() ) { ?>
-<?php if ($iis7_permalinks) :
+<?php if ( $iis7_permalinks ) :
 	if ( isset($_POST['submit']) && $permalink_structure && ! $usingpi && ! $writable ) :
 		if ( file_exists($home_path . 'web.config') ) : ?>
 <p><?php _e('If your <code>web.config</code> file were <a href="http://codex.wordpress.org/Changing_File_Permissions">writable</a>, we could do this automatically, but it isn&#8217;t so this is the url rewrite rule you should have in your <code>web.config</code> file. Click in the field and press <kbd>CTRL + a</kbd> to select all. Then insert this rule inside of the <code>/&lt;configuration&gt;/&lt;system.webServer&gt;/&lt;rewrite&gt;/&lt;rules&gt;</code> element in <code>web.config</code> file.') ?></p>