diff --git a/Corefile b/Corefile
index 86a2362..4b66441 100644
--- a/Corefile
+++ b/Corefile
@@ -4,7 +4,7 @@
     cancel
 
     view docker {
-        expr name() matches '^[a-z]+\\.docker\\.$'
+        expr name() matches '^[a-zA-Z0-9-_]+\\.docker\\.$'
     }
 
     rewrite name suffix .docker . answer auto