diff --git a/system/proj/proj.SlackBuild b/system/proj/proj.SlackBuild
index 676e7d3586..84d9344343 100644
--- a/system/proj/proj.SlackBuild
+++ b/system/proj/proj.SlackBuild
@@ -5,10 +5,19 @@
 
 PRGNAM=proj
 VERSION=${VERSION:-4.6.0}
-ARCH=${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-$VERSION
@@ -23,6 +32,9 @@ elif [ "$ARCH" = "i686" ]; then
 elif [ "$ARCH" = "x86_64" ]; then
   SLKCFLAGS="-O2 -fPIC"
   LIBDIRSUFFIX="64"
+else
+  SLKCFLAGS="-O2"
+  LIBDIRSUFFIX=""
 fi
 
 set -e