diff --git a/testing/regtest.cc b/testing/regtest.cc

index 12b712e..8219cc0 100644

--- a/testing/regtest.cc

+++ b/testing/regtest.cc

@@ -12,7 +12,7 @@ public:

     Options() : encode_srcwin_maxsz(1<<20), 

 		block_size(Constants::BLOCK_SIZE),

 		size_known(false) { }

-    size_t encode_srcwin_maxsz;

+    uint64_t encode_srcwin_maxsz;

     size_t block_size;

     bool size_known;

   };