diff --git a/html5lib/constants.py b/html5lib/constants.py
index 4f967cb6..c0db14f1 100644
--- a/html5lib/constants.py
+++ b/html5lib/constants.py
@@ -2939,6 +2939,7 @@
 
 
 class DataLossWarning(UserWarning):
+    """Raised when the current tree is unable to represent the input data"""
     pass