diff --git a/SystemInformation.hxx.in b/SystemInformation.hxx.in
index db23fe70ff3f720c9aab93a6ca43e365f24f0314..b6ebe6aee50b25e80cea1199580b8e6d9a7dc993 100644
--- a/SystemInformation.hxx.in
+++ b/SystemInformation.hxx.in
@@ -19,6 +19,7 @@
 # define kwsys_ios @KWSYS_NAMESPACE@_ios
 #endif
 #include <@KWSYS_NAMESPACE@/stl/string>
+#include <stddef.h> /* size_t */
 
 namespace @KWSYS_NAMESPACE@
 {