diff --git a/Source/kwsys/RegularExpression.hxx.in b/Source/kwsys/RegularExpression.hxx.in
index 9af53d300..a7d0b5057 100644
--- a/Source/kwsys/RegularExpression.hxx.in
+++ b/Source/kwsys/RegularExpression.hxx.in
@@ -281,7 +281,7 @@ private:
   char  regstart;                       // Internal use only
   char  reganch;                        // Internal use only
   const char* regmust;                  // Internal use only
-  unsigned long regmlen;                // Internal use only
+  size_t regmlen;                // Internal use only
   char* program;   
   int   progsize;
   const char* searchstring;