diff --git a/lib/moxml/xml_utils.rb b/lib/moxml/xml_utils.rb
index 2c93048..c226ec5 100644
--- a/lib/moxml/xml_utils.rb
+++ b/lib/moxml/xml_utils.rb
@@ -81,7 +81,7 @@ def validate_uri(uri, mode: :strict)
     end
 
     def validate_prefix(prefix)
-      return if prefix.match?(/\A[a-zA-Z_][\w-]*\z/)
+      return if prefix.match?(/\A[a-zA-Z_][\w.\-]*\z/)
 
       raise ValidationError, "Invalid namespace prefix: #{prefix}"
     end