diff --git a/tests/functional/external-builders.sh b/tests/functional/external-builders.sh
new file mode 100644
index 000000000..4c1d5636a
--- /dev/null
+++ b/tests/functional/external-builders.sh
@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+TODO_NixOS
+
+needLocalStore "'--external-builders' can’t be used with the daemon"
+
+expr="$TEST_ROOT/expr.nix"
+cat > "$expr" <<EOF
+with import ${config_nix};
+mkDerivation {
+  name = "external";
+  system = "x68_46-xunil";
+  buildCommand = ''
+    echo xyzzy
+    printf foo > \$out
+  '';
+}
+EOF
+
+external_builder="$TEST_ROOT/external-builder.sh"
+cat > "$external_builder" <<EOF
+#! $SHELL -e
+
+PATH=$PATH
+
+[[ "\$1" = bla ]]
+
+system="\$(jq -r .system < "\$2")"
+builder="\$(jq -r .builder < "\$2")"
+args="\$(jq -r '.args | join(" ")' < "\$2")"
+export buildCommand="\$(jq -r .env.buildCommand < "\$2")"
+export out="\$(jq -r .env.out < "\$2")"
+[[ \$system = x68_46-xunil ]]
+
+printf "\2\n"
+
+# In a real external builder, we would now call something like qemu to emulate the system.
+"\$builder" \$args
+
+printf bar >> \$out
+EOF
+chmod +x "$external_builder"
+
+nix build -L --file "$expr" --out-link "$TEST_ROOT/result" \
+  --extra-experimental-features external-builders \
+  --external-builders "[{\"systems\": [\"x68_46-xunil\"], \"args\": [\"bla\"], \"program\": \"$external_builder\"}]"
+
+[[ $(cat "$TEST_ROOT/result") = foobar ]]
diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index 368f60452..6f649c836 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -174,6 +174,7 @@ suites = [
       'extra-sandbox-profile.sh',
       'help.sh',
       'symlinks.sh',
+      'external-builders.sh',
     ],
     'workdir' : meson.current_source_dir(),
   },