diff --git a/GenericIO.cxx b/GenericIO.cxx
index 364b65463d5ee3e33c2ba827aa7796e6a3a82282..bc6ccec877c72a2ef92443a8c977b7d21f3fa24c 100644
--- a/GenericIO.cxx
+++ b/GenericIO.cxx
@@ -538,6 +538,7 @@ void GenericIO::write() {
 #endif
          if (!sz_initialized) {
            SZ_Init(NULL);
+           confparams_cpr->szMode = 0; // Best-speed mode.
            sz_initialized = true;
          }