diff --git a/core/XdmfHDF5Controller.hpp b/core/XdmfHDF5Controller.hpp
index c5c15d0a..496cc80d 100644
--- a/core/XdmfHDF5Controller.hpp
+++ b/core/XdmfHDF5Controller.hpp
@@ -27,13 +27,14 @@
 // C Compatible Includes
 #include "XdmfCore.hpp"
 #include "XdmfHeavyDataController.hpp"
+#include <cstdint>
 
 // So that hdf5 does not need to be included in the header files
 // It would add a dependancy to programs that use Xdmf
 #ifndef _H5Ipublic_H
   #ifndef XDMF_HID_T
   #define XDMF_HID_T
-    typedef int hid_t;
+    typedef int64_t hid_t;
   #endif
 #endif
 
diff --git a/core/XdmfHDF5Writer.hpp b/core/XdmfHDF5Writer.hpp
index cfbec6f4..f83aa0de 100644
--- a/core/XdmfHDF5Writer.hpp
+++ b/core/XdmfHDF5Writer.hpp
@@ -28,13 +28,14 @@
 #include "XdmfCore.hpp"
 #include "XdmfHeavyDataWriter.hpp"
 #include "XdmfHeavyDataController.hpp"
+#include <cstdint>
 
 // So that hdf5 does not need to be included in the header files
 // It would add a dependancy to programs that use Xdmf
 #ifndef _H5Ipublic_H
   #ifndef XDMF_HID_T
   #define XDMF_HID_T
-    typedef int hid_t;
+    typedef int64_t hid_t;
   #endif
 #endif