diff --git a/Source/kwsys/Directory.cxx b/Source/kwsys/Directory.cxx
index 5198ef894..d8a0b8e6c 100644
--- a/Source/kwsys/Directory.cxx
+++ b/Source/kwsys/Directory.cxx
@@ -48,7 +48,7 @@ Directory::~Directory()
 //----------------------------------------------------------------------------
 unsigned long Directory::GetNumberOfFiles()
 {
-  return this->Internal->Files.size();
+  return static_cast<unsigned long>(this->Internal->Files.size());
 }
 
 //----------------------------------------------------------------------------