diff --git a/diskimage_builder/lib/outfilter.py b/diskimage_builder/lib/outfilter.py
index 71c196d5..770742c2 100644
--- a/diskimage_builder/lib/outfilter.py
+++ b/diskimage_builder/lib/outfilter.py
@@ -26,7 +26,7 @@ import datetime
 import re
 import sys
 
-IGNORE_LINES = re.compile('(set \+o|xtrace)')
+IGNORE_LINES = re.compile(r'(set \+o|xtrace)')
 
 
 def get_options():