--- a/cubicweb/web/propertysheet.py	Wed Apr 10 17:59:17 2019 +0000
+++ b/cubicweb/web/propertysheet.py	Thu Apr 18 04:34:34 2019 +0000
@@ -47,7 +47,7 @@
         self.reset()
         context['sheet'] = self
         context['lazystr'] = self.lazystr
-        self._percent_rgx = re.compile('%(?!\()')
+        self._percent_rgx = re.compile(r'%(?!\()')
 
     def lazystr(self, str):
         return lazystr(str, self)