diff --git a/include/cantera/base/ctml.h b/include/cantera/base/ctml.h
index 50b245a88..cac708661 100644
--- a/include/cantera/base/ctml.h
+++ b/include/cantera/base/ctml.h
@@ -212,7 +212,7 @@ void addFloatArray(Cantera::XML_Node& node,  const std::string& titleString,
  *                    parameter. The default is the special double,
  *                    Cantera::Undef, which means to ignore the entry.
  */
-void addNamedFloatArray(Cantera::XML_Node& parentNode, const std::string& name, const int n,
+void addNamedFloatArray(Cantera::XML_Node& parentNode, const std::string& name, const size_t n,
                         const doublereal* const vals, const std::string units = "",
                         const std::string type = "",
                         const doublereal minval = Cantera::Undef,
diff --git a/include/cantera/base/xml.h b/include/cantera/base/xml.h
index fff9e3732..22406c8ca 100644
--- a/include/cantera/base/xml.h
+++ b/include/cantera/base/xml.h
@@ -280,6 +280,9 @@ public:
     void addAttribute(const std::string& attrib, const doublereal value,
                       const std::string& fmt="%g");
 
+    //! Add an unsigned integer attribute
+    void addAttribute(const std::string& attrib, size_t value);
+
     //! The operator[] is overloaded to provide a lookup capability
     //! on attributes for the current XML element.
     /*!
diff --git a/src/base/ctml.cpp b/src/base/ctml.cpp
index 06c70a156..e6d04e16d 100644
--- a/src/base/ctml.cpp
+++ b/src/base/ctml.cpp
@@ -95,13 +95,13 @@ void addFloatArray(Cantera::XML_Node& node, const std::string& title, const size
     }
 }
 
-void addNamedFloatArray(Cantera::XML_Node& node, const std::string& name, const int n,
+void addNamedFloatArray(Cantera::XML_Node& node, const std::string& name, const size_t n,
                         const doublereal* const vals, const std::string units,
                         const std::string type, const doublereal minval,
                         const doublereal maxval)
 {
     std::string v = "";
-    for (int i = 0; i < n; i++) {
+    for (size_t i = 0; i < n; i++) {
         v += fp2str(vals[i],FP_Format);
         if (i == n-1) {
             v += "\n";
diff --git a/src/base/xml.cpp b/src/base/xml.cpp
index b6839f039..7487c61d5 100644
--- a/src/base/xml.cpp
+++ b/src/base/xml.cpp
@@ -501,6 +501,11 @@ void XML_Node::addAttribute(const std::string& attrib_,
     m_attribs[attrib_] = fp2str(value_, fmt);
 }
 
+void XML_Node::addAttribute(const std::string& attrib_, const size_t value_)
+{
+    m_attribs[attrib_] = int2str(value_);
+}
+
 std::string XML_Node::operator[](const std::string& attr) const
 {
     return attrib(attr);