diff --git a/core/src/main/java/org/apache/struts2/dispatcher/mapper/DefaultActionMapper.java b/core/src/main/java/org/apache/struts2/dispatcher/mapper/DefaultActionMapper.java
index 1396025fc..005f9f201 100644
--- a/core/src/main/java/org/apache/struts2/dispatcher/mapper/DefaultActionMapper.java
+++ b/core/src/main/java/org/apache/struts2/dispatcher/mapper/DefaultActionMapper.java
@@ -120,7 +120,7 @@ public class DefaultActionMapper implements ActionMapper {
     protected boolean allowSlashesInActionNames = false;
     protected boolean alwaysSelectFullNamespace = false;
     protected PrefixTrie prefixTrie = null;
-    protected Pattern allowedActionNames = Pattern.compile("^[a-zA-Z0-9_!/\\-]+((.htm[l]?)|(.action))?$");
+    protected Pattern allowedActionNames = Pattern.compile("^[a-zA-Z0-9_!/\\-]*((.htm[l]?)|(.action))?$");
     private boolean allowActionPrefix = false;
     private boolean allowActionCrossNamespaceAccess = false;