diff --git a/idea/base.py b/idea/base.py
index e5e234209fb60d273f604e491bcb05dd8cac9016..db5151b6512cc620916033460bd0c57078316cbc 100644
--- a/idea/base.py
+++ b/idea/base.py
@@ -26,7 +26,7 @@ event_tag_re = re.compile(r"^[a-zA-Z0-9_-]+(?:\.[a-zA-Z0-9_-]+)?$")
 tag_re = re.compile(r"^[a-zA-Z0-9_-]+$")
 
 timestamp_re = re.compile(r"^([0-9]{4})-([0-9]{2})-([0-9]{2})[Tt ]([0-9]{2}):([0-9]{2}):([0-9]{2})(?:\.([0-9]+))?([Zz]|(?:[+-][0-9]{2}:[0-9]{2}))$")
-duration_re = re.compile("(?:([0-9]+)[Dd])?([0-9]{2}):([0-9]{2}):([0-9]{2})(?:\.([0-9]+))?$")
+duration_re = re.compile(r"(?:([0-9]+)[Dd])?([0-9]{2}):([0-9]{2}):([0-9]{2})(?:\.([0-9]+))?$")
 
 
 def source_target_dict_typedef(flavour, list_flavour, addon=None):