diff --git a/src/calibre/gui2/lrf_renderer/text.py b/src/calibre/gui2/lrf_renderer/text.py
index 2f050a2e89..9231a17325 100644
--- a/src/calibre/gui2/lrf_renderer/text.py
+++ b/src/calibre/gui2/lrf_renderer/text.py
@@ -315,6 +315,8 @@ class TextBlock(object):
             raw = raw[pos:]
             if line_filled:
                 self.end_line()
+            if not pos:
+                break
 
     def __iter__(self):
         for line in self.lines: