diff --git a/Makefile b/Makefile
index 531563e..64e2003 100644
--- a/Makefile
+++ b/Makefile
@@ -48,7 +48,7 @@ endif
 
 ETC_LOCALTIME := $(realpath /etc/localtime)
 
-HOST_ARCH := $(shell arch)
+HOST_ARCH ?= $(shell arch)
 ifeq ($(HOST_ARCH),x86_64)
     DOCKER_PLATFORM := "linux/amd64"
 else ifeq ($(HOST_ARCH),arm64)
diff --git a/build.sh b/build.sh
index acacb44..9c606bd 100755
--- a/build.sh
+++ b/build.sh
@@ -36,15 +36,8 @@ DOCKER_BUILD="docker build"
 DOCKER_INSPECT="docker inspect"
 DOCKER_FLAGS="--force-rm=true"
 
-HOST_ARCH=`arch`
-if [[ $HOST_ARCH == "x86_64" ]]; then
-    DOCKER_PLATFORM="linux/amd64"
-elif [[ $HOST_ARCH == "arm64" ]]; then
-    DOCKER_PLATFORM="linux/arm64/v8"
-else
-    echo "Unsupported host architecture: $HOST_ARCH"
-    exit 1
-fi
+# By default use host architecture
+: "${HOST_ARCH:=`arch`}"
 
 # Special variables to be passed through Docker to the build scripts
 : "${SCM}"
@@ -182,7 +175,7 @@ show_help()
                             | sort \
                             | tr "\n" "|")
     cat <<EOF
-    build.sh [-r] [-v] [-p] -b [sel4|camkes|l4v] -s [$available_software] -s ... -e MAKE_CACHES=no -e ...
+    build.sh [-r] [-v] [-p] [-a arch] -b [sel4|camkes|l4v] -s [$available_software] -s ... -e MAKE_CACHES=no -e ...
 
      -r     Rebuild docker images (don't use the docker cache)
      -v     Verbose mode
@@ -190,6 +183,7 @@ show_help()
      -e     Build arguments (NAME=VALUE) to docker build. Use a -e for each build arg.
      -p     Pull base image first. Rather than build the base image,
             get it from the web first
+     -a     Supply x86_64 for building Intel images, and arm64 for Arm images
 
     Sneaky hints:
      - To build 'prebuilt' images, you can run:
@@ -206,7 +200,7 @@ img_to_build=
 software_to_apply=
 pull_base_first=
 
-while getopts "h?pvb:rs:e:" opt
+while getopts "h?pvb:rs:e:a:" opt
 do
     case "$opt" in
     h|\?)
@@ -225,12 +219,27 @@ do
         ;;
     e)  build_args="$build_args\n$OPTARG"
         ;;
+    a)  HOST_ARCH="$OPTARG"
+        ;;
     :)  echo "Option -$opt requires an argument." >&2
         exit 1
         ;;
     esac
 done
 
+if [[ $HOST_ARCH == "x86_64" ]]; then
+    DOCKER_PLATFORM="linux/amd64"
+elif [[ $HOST_ARCH == "amd64" ]]; then
+    DOCKER_PLATFORM="linux/amd64"
+elif [[ $HOST_ARCH == "arm64" ]]; then
+    DOCKER_PLATFORM="linux/arm64/v8"
+else
+    echo "Unsupported host architecture: $HOST_ARCH"
+    exit 1
+fi
+
+echo "Building for $DOCKER_PLATFORM"
+
 if [ -z "$img_to_build" ]
 then
     echo "You need to supply a \`-b\`" >&2