diff --git a/mod.php b/mod.php
index 62edac7c..792efbb0 100644
--- a/mod.php
+++ b/mod.php
@@ -374,21 +374,36 @@
 					$query->bindValue(':theme', $_theme);
 					$query->execute() or error(db_error($query));
 					
+					$result = true;
 					$body = '';
 					if(isset($theme['install_callback'])) {
 						$ret = $theme['install_callback']($theme['config']);
-						if($ret && !empty($ret))
+						if($ret && !empty($ret)) {
+							if(is_array($ret) && count($ret) == 2) {
+								$result = $ret[0];
+								$ret = $ret[1];
+							}
 							$body .= '<div style="border:1px dashed maroon;padding:20px;margin:auto;max-width:800px">' . $ret . '</div>';
+						}
 					}
-					$body .= '<p style="text-align:center">Successfully installed and built theme.</p>' .
-						'<p style="text-align:center"><a href="?/themes">Go back to themes</a>.</p>';
+					
+					if($result) {
+						$body .= '<p style="text-align:center">Successfully installed and built theme.</p>';
+					} else {
+						// install failed
+						$query = prepare("DELETE FROM `theme_settings` WHERE `theme` = :theme");
+						$query->bindValue(':theme', $_theme);
+						$query->execute() or error(db_error($query));
+					}
+					
+					$body .= '<p style="text-align:center"><a href="?/themes">Go back to themes</a>.</p>';
 					
 					// Build themes
 					rebuildThemes('all');
 					
 					echo Element('page.html', Array(
 						'config'=>$config,
-						'title'=>'Installed "' . utf8tohtml($theme['name']) . '"',
+						'title'=>($result ? 'Installed "' . utf8tohtml($theme['name']) . '"' : 'Installation failed!'),
 						'body'=>$body,
 						'mod'=>true
 						)
diff --git a/templates/themes/categories/info.php b/templates/themes/categories/info.php
index 0090f39d..108cc254 100644
--- a/templates/themes/categories/info.php
+++ b/templates/themes/categories/info.php
@@ -27,4 +27,16 @@ Requires $config[\'boards\'] and $config[\'categories\'].';
 	
 	// Unique function name for building everything
 	$theme['build_function'] = 'categories_build';
+	
+	$theme['install_callback'] = 'categories_install';
+	if(!function_exists('categories_install')) {
+		function categories_install($settings) {
+			global $config;
+			
+			if(!isset($config['boards']) || !isset($config['categories'])) {
+				return Array(false, '<h2>Prerequisites not met!</h2>' . 
+					'This theme requires $config[\'boards\'] and $config[\'categories\'] to be set.');
+			}
+		}
+	}
 ?>
diff --git a/templates/themes/categories/theme.php b/templates/themes/categories/theme.php
index de1b4a5b..d48c150a 100644
--- a/templates/themes/categories/theme.php
+++ b/templates/themes/categories/theme.php
@@ -121,27 +121,31 @@
 				'<li><a class="system" href="javascript:parent.removeFrames()">[Remove Frames]</a></li>' .
 			'</ul></fieldset>';
 			
-			for($cat = 0; $cat < count($config['categories']); $cat++) {
-				$body .= '<fieldset><legend>' . $config['categories'][$cat] . '</legend><ul>';
+			if(isset($config['categories'])) {
+				for($cat = 0; $cat < count($config['categories']); $cat++) {
+					$body .= '<fieldset><legend>' . $config['categories'][$cat] . '</legend><ul>';
 				
-				foreach($config['boards'][$cat] as &$board) {
-					$body .= '<li><a href="' .
-						sprintf($config['board_path'], $board) .
-					'">' . boardTitle($board) . '</a></li>';
+					foreach($config['boards'][$cat] as &$board) {
+						$body .= '<li><a href="' .
+							sprintf($config['board_path'], $board) .
+						'">' . boardTitle($board) . '</a></li>';
+					}
+				
+					$body .= '</ul></fieldset>';
 				}
-				
-				$body .= '</ul></fieldset>';
 			}
 			
-			foreach($config['custom_categories'] as $name => &$group) {
-				$body .= '<fieldset><legend>' . $name . '</legend><ul>';
+			if(isset($config['custom_categories'])) {
+				foreach($config['custom_categories'] as $name => &$group) {
+					$body .= '<fieldset><legend>' . $name . '</legend><ul>';
 				
-				foreach($group as $title => &$url) {
-					$body .= '<li><a href="' . $url .
-					'">' . $title . '</a></li>';
+					foreach($group as $title => &$url) {
+						$body .= '<li><a href="' . $url .
+						'">' . $title . '</a></li>';
+					}
+				
+					$body .= '</ul></fieldset>';
 				}
-				
-				$body .= '</ul></fieldset>';
 			}
 			
 			// Finish page