diff --git a/ShellB3/shallbethree.sh b/ShellB3/shallbethree.sh
index 76a79aa05f535edcd2620600fa218ca5dcdced64..3777c3c455576cf48658d987ac9fca641d62e4aa 100755
--- a/ShellB3/shallbethree.sh
+++ b/ShellB3/shallbethree.sh
@@ -502,8 +502,8 @@ mk_hdf5() {
   echo building hdf5 for $BASE
   test -n "$SZLIB" && SZOPTS="--with-szlib=$SZLIB" || SZOPTS=""
   (cd build/hdf5-${HDF5VER} \
-   && ./configure --prefix=$BASE --enable-shared --with-pic --with-zlib=$ZLIB --with-pthread $SZOPTS \
-   && make \
+   && ./configure --prefix=$BASE --enable-shared --enable-cxx --with-pic --with-zlib=$ZLIB --with-pthread $SZOPTS \
+   && make -j8 \
    && make install ) \
    || oops "hdf5 build failed"
   # fix RPATH forcing issue