diff --git a/.travis.yml b/.travis.yml
index 016088a..b9e7370 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,12 @@ sudo: false
 
 language: cpp
 
+arch:
+   - amd64
+   - arm64
+   - ppc64le
+   - s390x
+
 compiler:
     - gcc
 
diff --git a/test/run_tests.bash b/test/run_tests.bash
index b87f45d..757a164 100755
--- a/test/run_tests.bash
+++ b/test/run_tests.bash
@@ -24,10 +24,13 @@ FAIL alpha1.png alpha2.png
 EOF
 }
 
+echo "*** tmpdir: ${tmpdir:=/tmp}"
+
 # Change to test directory
-readonly script_directory=$(dirname "$0")
+echo "*** script_directory: ${script_directory:=$(dirname "$0")}"
 cd "$script_directory"
 
+if [ -z "${pdiff:=}" ]; then
 found=0
 for d in ../build .. ../obj*; do
     pdiff="$d/perceptualdiff"
@@ -40,9 +43,9 @@ done
 if [ $found = 0 ]; then
     echo 'perceptualdiff must be built and exist in the repository root or the "build" directory'
     exit 1
-else
-    echo "*** testing executable binary $pdiff"
 fi
+fi
+echo "*** testing executable binary $pdiff"
 
 #------------------------------------------------------------------------------
 
@@ -77,19 +80,19 @@ fi
 "$pdiff" --help | grep -i 'usage'
 
 rm -f diff.png
-"$pdiff" --output diff.png --verbose fish[12].png 2>&1 | grep -q 'FAIL'
-ls diff.png
-rm -f diff.png
+"$pdiff" --output ${tmpdir}/diff.png --verbose fish{1,2}.png 2>&1 | grep -q 'FAIL'
+ls ${tmpdir}/diff.png
+rm -f ${tmpdir}/diff.png
 
-head fish1.png > fake.png
-"$pdiff" --verbose fish1.png fake.png 2>&1 | grep -q 'Failed to load'
-rm -f fake.png
+head fish1.png > ${tmpdir}/fake.png
+"$pdiff" --verbose fish1.png ${tmpdir}/fake.png 2>&1 | grep -q 'Failed to load'
+rm -f ${tmpdir}/fake.png
 
-mkdir -p unwritable.png
-"$pdiff" --output unwritable.png --verbose fish[12].png 2>&1 | grep -q 'Failed to save'
-rmdir unwritable.png
+mkdir -p ${tmpdir}/unwritable.png
+"$pdiff" --output ${tmpdir}/unwritable.png --verbose fish{1,2}.png 2>&1 | grep -q 'Failed to save'
+rmdir ${tmpdir}/unwritable.png
 
-"$pdiff" fish[12].png --output foo 2>&1 | grep -q 'unknown filetype'
+"$pdiff" fish{1,2}.png --output ${tmpdir}/foo 2>&1 | grep -q 'unknown filetype'
 "$pdiff" --verbose fish1.png 2>&1 | grep -q 'Not enough'
 "$pdiff" --down-sample -3 fish1.png Aqsis_vase.png 2>&1 | grep -q 'Invalid'
 "$pdiff" --threshold -3 fish1.png Aqsis_vase.png 2>&1 | grep -q 'Invalid'
@@ -97,7 +100,7 @@ rmdir unwritable.png
 "$pdiff" --verbose --scale fish1.png Aqsis_vase.png 2>&1 | grep -q 'FAIL'
 "$pdiff" --down-sample 2 fish1.png Aqsis_vase.png 2>&1 | grep -q 'FAIL'
 "$pdiff"  /dev/null /dev/null 2>&1 | grep -q 'Unknown filetype'
-"$pdiff" --verbose --sum-errors fish[12].png 2>&1 | grep -q 'sum'
+"$pdiff" --verbose --sum-errors fish{1,2}.png 2>&1 | grep -q 'sum'
 "$pdiff" --color-factor .5 -threshold 1000 --gamma 3 --luminance 90 cam_mb_ref.tif cam_mb.tif
 "$pdiff" --verbose -down-sample 30 -scale --luminance-only --fov 80 cam_mb_ref.tif cam_mb.tif
 "$pdiff" --fov wrong fish1.png fish1.png 2>&1 | grep -q 'Invalid argument'