diff --git a/r2/r2/lib/cssfilter.py b/r2/r2/lib/cssfilter.py
index fc6450e6c..0f08a6c65 100644
--- a/r2/r2/lib/cssfilter.py
+++ b/r2/r2/lib/cssfilter.py
@@ -240,7 +240,7 @@ def validate_css(string):
         return ('',ValidationReport())
 
     report = ValidationReport(string)
-    
+
     # avoid a very expensive parse
     max_size_kb = 100;
     if len(string) > max_size_kb * 1024:
@@ -248,6 +248,9 @@ def validate_css(string):
                                        % dict (max_size = max_size_kb))))
         return (string, report)
 
+    if '\\' in string:
+        report.append(ValidationError(_("if you need backslashes, you're doing it wrong")))
+
     try:
         parsed = p.parseString(string)
     except DOMException,e: