diff --git a/network/allmydata-tahoe/allmydata-tahoe.SlackBuild b/network/allmydata-tahoe/allmydata-tahoe.SlackBuild
index 2af7328fe0..eaffe1d191 100644
--- a/network/allmydata-tahoe/allmydata-tahoe.SlackBuild
+++ b/network/allmydata-tahoe/allmydata-tahoe.SlackBuild
@@ -24,10 +24,19 @@
 
 PRGNAM=allmydata-tahoe
 VERSION=${VERSION:-1.6.1}
-ARCH=${ARCH:-i486}
 BUILD=${BUILD:-1}
 TAG=${TAG:-_SBo}
 
+# Automatically determine the architecture we're building on:
+if [ -z "$ARCH" ]; then
+  case "$( uname -m )" in
+    i?86) ARCH=i486 ;;
+    arm*) ARCH=arm ;;
+    # Unless $ARCH is already set, use uname -m for all other archs:
+       *) ARCH=$( uname -m ) ;;
+  esac
+fi
+
 CWD=$(pwd)
 TMP=${TMP:-/tmp/SBo}
 PKG=$TMP/package-$PRGNAM