diff --git a/external_deps/build.sh b/external_deps/build.sh
index f7201ebbde..baa8b2359d 100755
--- a/external_deps/build.sh
+++ b/external_deps/build.sh
@@ -38,6 +38,8 @@ OPUS_BASEURL='https://downloads.xiph.org/releases/opus'
 OPUSFILE_BASEURL='https://downloads.xiph.org/releases/opus'
 # No index.
 NACLSDK_BASEURL='https://storage.googleapis.com/nativeclient-mirror/nacl/nacl_sdk'
+# No index.
+NACLRUNTIME_BASEURL='https://api.github.com/repos/DaemonEngine/native_client/zipball'
 NCURSES_BASEURL='https://ftpmirror.gnu.org/gnu/ncurses'
 WASISDK_BASEURL='https://github.com/WebAssembly/wasi-sdk/releases'
 WASMTIME_BASEURL='https://github.com/bytecodealliance/wasmtime/releases'
@@ -60,6 +62,7 @@ VORBIS_VERSION=1.3.7
 OPUS_VERSION=1.4
 OPUSFILE_VERSION=0.12
 NACLSDK_VERSION=44.0.2403.155
+NACLRUNTIME_REVISION=2aea5fcfce504862a825920fcaea1a8426afbd6f
 NCURSES_VERSION=6.2
 WASISDK_VERSION=16.0
 WASMTIME_VERSION=2.0.2
@@ -790,9 +793,15 @@ build_naclsdk() {
 
 	"${download_only}" && return
 
-	cp pepper_*"/tools/sel_ldr_${NACLSDK_ARCH}${EXE}" "${PREFIX}/nacl_loader${EXE}"
 	cp pepper_*"/tools/irt_core_${NACLSDK_ARCH}.nexe" "${PREFIX}/irt_core-${DAEMON_ARCH}.nexe"
 	case "${PLATFORM}" in
+	linux-amd64-*)
+		;; # Get sel_ldr from naclruntime package
+	*)
+		cp pepper_*"/tools/sel_ldr_${NACLSDK_ARCH}${EXE}" "${PREFIX}/nacl_loader${EXE}"
+		;;
+	esac
+	case "${PLATFORM}" in
 	windows-i686-*|*-amd64-*)
 		cp pepper_*"/toolchain/${NACLSDK_PLATFORM}_x86_newlib/bin/x86_64-nacl-gdb${EXE}" "${PREFIX}/nacl-gdb${EXE}"
 
@@ -816,7 +825,11 @@ build_naclsdk() {
 		cp pepper_*"/tools/sel_ldr_x86_64.exe" "${PREFIX}/nacl_loader-amd64.exe"
 		cp pepper_*"/tools/irt_core_x86_64.nexe" "${PREFIX}/irt_core-amd64.nexe"
 		;;
-	linux-amd64-*|linux-i686-*)
+	linux-amd64-*)
+		# Fix permissions on a few files which deny access to non-owner
+		chmod 644 "${PREFIX}/irt_core-${DAEMON_ARCH}.nexe"
+		;;
+	linux-i686-*)
 		cp pepper_*"/tools/nacl_helper_bootstrap_${NACLSDK_ARCH}" "${PREFIX}/nacl_helper_bootstrap"
 		# Fix permissions on a few files which deny access to non-owner
 		chmod 644 "${PREFIX}/irt_core-${DAEMON_ARCH}.nexe"
@@ -843,6 +856,31 @@ build_naclsdk() {
 	esac
 }
 
+# Only builds nacl_loader and nacl_helper_bootstrap for now, not IRT.
+build_naclruntime() {
+	case "${PLATFORM}" in
+	linux-amd64-*)
+		local NACL_ARCH=x86-64
+		;;
+	*)
+		log error 'Unsupported platform for naclruntime'
+		;;
+	esac
+
+	local dir_name="DaemonEngine-native_client-${NACLRUNTIME_REVISION:0:7}"
+	local archive_name="native_client-${NACLRUNTIME_REVISION}.zip"
+
+	download_extract naclruntime "${archive_name}" \
+		"{$NACLRUNTIME_BASEURL}/${NACLRUNTIME_REVISION}"
+
+	"${download_only}" && return
+
+	cd "${dir_name}"
+	scons --mode=opt-linux "platform=${NACL_ARCH}" werror=0 sysinfo=0 sel_ldr
+	cp "scons-out/opt-linux-${NACL_ARCH}/staging/nacl_helper_bootstrap" "${PREFIX}/nacl_helper_bootstrap"
+	cp "scons-out/opt-linux-${NACL_ARCH}/staging/sel_ldr" "${PREFIX}/nacl_loader"
+}
+
 # The import libraries generated by MinGW seem to have issues, so we use LLVM's version instead.
 # So LLVM must be installed, e.g. 'sudo apt install llvm'
 build_genlib() {
@@ -1117,8 +1155,8 @@ all_windows_i686_mingw_packages="${base_windows_amd64_mingw_packages}"
 base_macos_amd64_default_packages='pkgconfig nasm gmp nettle sdl2 glew png jpeg webp openal ogg vorbis opus opusfile naclsdk'
 all_macos_amd64_default_packages="${base_macos_amd64_default_packages}"
 
-base_linux_amd64_default_packages='naclsdk'
-all_linux_amd64_default_packages='zlib gmp nettle curl sdl2 glew png jpeg webp openal ogg vorbis opus opusfile naclsdk'
+base_linux_amd64_default_packages='naclsdk naclruntime'
+all_linux_amd64_default_packages='zlib gmp nettle curl sdl2 glew png jpeg webp openal ogg vorbis opus opusfile naclsdk naclruntime'
 
 base_linux_i686_default_packages="${base_linux_amd64_default_packages}"
 all_linux_i686_default_packages="${all_linux_amd64_default_packages}"
@@ -1224,6 +1262,7 @@ fi
 
 # Enable parallel build
 export MAKEFLAGS="-j`nproc 2> /dev/null || sysctl -n hw.ncpu 2> /dev/null || echo 1`"
+export SCONSFLAGS="${MAKEFLAGS}"
 
 # Setup platform
 platform="${1}"; shift