diff --git a/book/build.sh b/book/build.sh
index 4d1e3e32c8..14063a5279 100755
--- a/book/build.sh
+++ b/book/build.sh
@@ -3,21 +3,16 @@ set -e
 
 cd "$(dirname "$0")"
 
-_() {
-  echo "--- $*"
-  "$@"
-}
-
 cargo_install_unless() {
   declare crate=$1
   shift
 
   "$@" > /dev/null 2>&1 || \
-    _ cargo install "$crate"
+    cargo install "$crate"
 }
 
 export PATH=$CARGO_HOME/bin:$PATH
 cargo_install_unless mdbook mdbook --help
 cargo_install_unless svgbob_cli svgbob --help
 
-_ make
+make -j"$(nproc)"