diff --git a/src/xalanc/XPath/XString.hpp b/src/xalanc/XPath/XString.hpp
index eb7f68046..10997308e 100644
--- a/src/xalanc/XPath/XString.hpp
+++ b/src/xalanc/XPath/XString.hpp
@@ -89,6 +89,7 @@ class XALAN_XPATH_EXPORT XString : public XStringBase
     set(const XalanDOMString&   theString)
     {
         m_value = theString;
+        ClearCachedNumber();
     }
 
     // These methods are inherited from XObject ...
diff --git a/src/xalanc/XPath/XStringBase.cpp b/src/xalanc/XPath/XStringBase.cpp
index 0861e6b5d..49fe77551 100644
--- a/src/xalanc/XPath/XStringBase.cpp
+++ b/src/xalanc/XPath/XStringBase.cpp
@@ -154,6 +154,11 @@ XStringBase::str() const
                 theBuffer);
 }
 
+void
+XStringBase::ClearCachedNumber()
+{
+    m_cachedNumberValue = 0.0;
+}
 
 
 }
diff --git a/src/xalanc/XPath/XStringBase.hpp b/src/xalanc/XPath/XStringBase.hpp
index 9b667ba9b..03b9c1b13 100644
--- a/src/xalanc/XPath/XStringBase.hpp
+++ b/src/xalanc/XPath/XStringBase.hpp
@@ -128,6 +128,9 @@ class XALAN_XPATH_EXPORT XStringBase : public XObject
     virtual void
     ProcessXObjectTypeCallback(XObjectTypeCallback&     theCallbackObject) const;
 
+    virtual void
+    ClearCachedNumber();
+
 private:
 
     friend class XObjectResultTreeFragProxyText;