diff --git a/go/build.sh b/go/build.sh
index c08eb37..6aad819 100755
--- a/go/build.sh
+++ b/go/build.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
 set -eu
 
-export MAKEFLAGS="-j$(nproc)"
+export MAKEFLAGS="-j${NPROC:-$(nproc)}"
 
 [ ! -d build/install-bootstrap ] && ./build_bootstrap.sh
 [ ! -d build/install-go ] && ./build_go.sh
diff --git a/go/build_go.sh b/go/build_go.sh
index a7a3660..854724f 100755
--- a/go/build_go.sh
+++ b/go/build_go.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
 set -eu
 
-version_go=1.13
+version_go=1.15
 
 dir_download="$PWD/download"
 mkdir -p build; cd build
diff --git a/go/download.sh b/go/download.sh
index a515ae2..315cf57 100755
--- a/go/download.sh
+++ b/go/download.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
 set -eu
 
-version_go=1.13  # https://golang.org/dl/
+version_go=1.15  # https://golang.org/dl/
 version_bootstrap=20171003  # https://golang.org/doc/install/source#go14
 
 mkdir -p download
diff --git a/go/download.sha256 b/go/download.sha256
index 81e1df6..cd475f3 100644
--- a/go/download.sha256
+++ b/go/download.sha256
@@ -1,2 +1,2 @@
-3fc0b8b6101d42efd7da1da3029c0a13f22079c0c37ef9730209d8ec665bf122  go1.13.src.tar.gz
+69438f7ed4f532154ffaf878f3dfd83747e7a00b70b3556eddabf7aaee28ac3a  go1.15.src.tar.gz
 f4ff5b5eb3a3cae1c993723f3eab519c5bae18866b5e5f96fe1102f0cb5c3e52  go1.4-bootstrap-20171003.tar.gz