diff --git a/lib/src/parse/stylesheet.dart b/lib/src/parse/stylesheet.dart
index afe741594..e1b87fa7b 100644
--- a/lib/src/parse/stylesheet.dart
+++ b/lib/src/parse/stylesheet.dart
@@ -1398,7 +1398,7 @@ abstract class StylesheetParser extends Parser {
     try {
       return Parser.parseIdentifier(namespace, logger: logger);
     } on SassFormatException {
-      error('Invalid Sass identifier "$namespace"', scanner.spanFrom(start));
+      error('The default namespace "$namespace" is not a valid Sass identifier.\n\nRecommendation: add an "as" clause to define an explicit namespace.', scanner.spanFrom(start));
     }
   }