diff --git a/scrapy/http/request/form.py b/scrapy/http/request/form.py
index 8ff394602..948ad05c9 100644
--- a/scrapy/http/request/form.py
+++ b/scrapy/http/request/form.py
@@ -85,7 +85,8 @@ def _get_form(response, formname, formid, formnumber, formxpath):
                 el = el.getparent()
                 if el is None:
                     break
-        raise ValueError('No <form> element found with %s' % formxpath)
+        encoded = formxpath if six.PY3 else formxpath.encode('unicode_escape')
+        raise ValueError('No <form> element found with %s' % encoded)
 
     # If we get here, it means that either formname was None
     # or invalid