diff --git a/tests/tarball.sh b/tests/tarball.sh
index ec810b4d715fd2f5a0984706cbd20b456d8cbf4f..7738b948d90bab9cec22137c1e0e853e3d4deb59 100644
--- a/tests/tarball.sh
+++ b/tests/tarball.sh
@@ -10,36 +10,28 @@ mkdir -p $tarroot
 cp dependencies.nix $tarroot/default.nix
 cp config.nix dependencies.builder*.sh $tarroot/
 
-tarball=$TEST_ROOT/tarball.tar.xz
-(cd $TEST_ROOT && tar c tarball) | xz > $tarball
+test_tarball() {
+    local ext="$1"
+    local compressor="$2"
 
-nix-env -f file://$tarball -qa --out-path | grep -q dependencies
+    tarball=$TEST_ROOT/tarball.tar$ext
+    (cd $TEST_ROOT && tar c tarball) | $compressor > $tarball
 
-nix-build -o $TEST_ROOT/result file://$tarball
+    nix-env -f file://$tarball -qa --out-path | grep -q dependencies
 
-nix-build -o $TEST_ROOT/result '<foo>' -I foo=file://$tarball
+    nix-build -o $TEST_ROOT/result file://$tarball
 
-nix-build -o $TEST_ROOT/result -E "import (fetchTarball file://$tarball)"
+    nix-build -o $TEST_ROOT/result '<foo>' -I foo=file://$tarball
 
-nix-instantiate --eval -E '1 + 2' -I fnord=file://no-such-tarball.tar.xz
-nix-instantiate --eval -E 'with <fnord/xyzzy>; 1 + 2' -I fnord=file://no-such-tarball.tar.xz
-(! nix-instantiate --eval -E '<fnord/xyzzy> 1' -I fnord=file://no-such-tarball.tar.xz)
+    nix-build -o $TEST_ROOT/result -E "import (fetchTarball file://$tarball)"
 
-nix-instantiate --eval -E '<fnord/config.nix>' -I fnord=file://no-such-tarball.tar.xz -I fnord=.
+    nix-instantiate --eval -E '1 + 2' -I fnord=file://no-such-tarball.tar$ext
+    nix-instantiate --eval -E 'with <fnord/xyzzy>; 1 + 2' -I fnord=file://no-such-tarball$ext
+    (! nix-instantiate --eval -E '<fnord/xyzzy> 1' -I fnord=file://no-such-tarball$ext)
 
-tarball=$TEST_ROOT/tarball.tar.gz
-(cd $TEST_ROOT && tar c tarball) | gzip > $tarball
+    nix-instantiate --eval -E '<fnord/config.nix>' -I fnord=file://no-such-tarball$ext -I fnord=.
+}
 
-nix-env -f file://$tarball -qa --out-path | grep -q dependencies
-
-nix-build -o $TEST_ROOT/result file://$tarball
-
-nix-build -o $TEST_ROOT/result '<foo>' -I foo=file://$tarball
-
-nix-build -o $TEST_ROOT/result -E "import (fetchTarball file://$tarball)"
-
-nix-instantiate --eval -E '1 + 2' -I fnord=file://no-such-tarball.tar.gz
-nix-instantiate --eval -E 'with <fnord/xyzzy>; 1 + 2' -I fnord=file://no-such-tarball.tar.gz
-(! nix-instantiate --eval -E '<fnord/xyzzy> 1' -I fnord=file://no-such-tarball.tar.gz)
-
-nix-instantiate --eval -E '<fnord/config.nix>' -I fnord=file://no-such-tarball.tar.gz -I fnord=.
+test_tarball '' cat
+test_tarball .xz xz
+test_tarball .gz gzip