diff --git a/libraries/libmp4v2/libmp4v2.SlackBuild b/libraries/libmp4v2/libmp4v2.SlackBuild
index 4e0cb54ae7..f76f721f1d 100644
--- a/libraries/libmp4v2/libmp4v2.SlackBuild
+++ b/libraries/libmp4v2/libmp4v2.SlackBuild
@@ -36,10 +36,19 @@
 PRGNAM=libmp4v2
 SRCNAM=mp4v2
 VERSION=1.9.1
-ARCH=${ARCH:-i486}
 BUILD=${BUILD:-3}
 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
@@ -54,6 +63,9 @@ elif [ "$ARCH" = "i686" ]; then
 elif [ "$ARCH" = "x86_64" ]; then
   SLKCFLAGS="-O2 -fPIC"
   LIBDIRSUFFIX="64"
+else
+  SLKCFLAGS="-O2"
+  LIBDIRSUFFIX=""
 fi
 
 set -e