diff --git a/lib-php/DebugHtml.php b/lib-php/DebugHtml.php
index 19221b43..ea3d514f 100644
--- a/lib-php/DebugHtml.php
+++ b/lib-php/DebugHtml.php
@@ -127,7 +127,7 @@ class Debug
 
     public static function printSQL($sSQL)
     {
-        echo '<p><tt><font color="#aaa">'.$sSQL.'</font></tt></p>'."\n";
+        echo '<p><tt><font color="#aaa">'.htmlspecialchars($sSQL).'</font></tt></p>'."\n";
     }
 
     private static function outputVar($mVar, $sPreNL)
@@ -170,11 +170,12 @@ class Debug
         }
 
         if (is_string($mVar)) {
-            echo "'$mVar'";
-            return strlen($mVar) + 2;
+            $sOut = "'$mVar'";
+        } else {
+            $sOut = (string)$mVar;
         }
 
-        echo (string)$mVar;
-        return strlen((string)$mVar);
+        echo htmlspecialchars($sOut);
+        return strlen($sOut);
     }
 }