diff --git a/extruct/rdfa.py b/extruct/rdfa.py
index 273b0b57..c313e2b6 100644
--- a/extruct/rdfa.py
+++ b/extruct/rdfa.py
@@ -85,7 +85,7 @@ def _replaceNS(self, prop, html_element, head_element):
 
         match = None
         if head_element.get("prefix"):
-            match = re.search(prefix + ": [^\s]+", head_element.get("prefix"))
+            match = re.search(prefix + r": [^\s]+", head_element.get("prefix"))
 
         # if namespace taken from prefix attribute in head tag
         if match: