diff --git a/CHANGELOG b/CHANGELOG
index 0b2809d87..fa19ae4b7 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,6 @@
 * 1.35.3 (2018-XX-XX)
 
+ * added missing else clause to avoid infinite loops
  * fixed .. (range operator) in sandbox policy
 
 * 1.35.2 (2018-03-03)
diff --git a/lib/Twig/Lexer.php b/lib/Twig/Lexer.php
index 4efdfb4ad..41211eb28 100644
--- a/lib/Twig/Lexer.php
+++ b/lib/Twig/Lexer.php
@@ -343,6 +343,9 @@ class Twig_Lexer implements Twig_LexerInterface
 
             $this->popState();
             ++$this->cursor;
+        } else {
+            // unlexable
+            throw new Twig_Error_Syntax(sprintf('Unexpected character "%s".', $this->code[$this->cursor]), $this->lineno, $this->source);
         }
     }