diff --git a/src/org/apache/xpath/jaxp/JAXPVariableStack.java b/src/org/apache/xpath/jaxp/JAXPVariableStack.java
index 4af13bf..d98638d 100644
--- a/src/org/apache/xpath/jaxp/JAXPVariableStack.java
+++ b/src/org/apache/xpath/jaxp/JAXPVariableStack.java
@@ -42,6 +42,7 @@
     private final XPathVariableResolver resolver;
 	
     public JAXPVariableStack(XPathVariableResolver resolver) {
+        super(2);
         this.resolver = resolver;
     }