diff --git a/tests/functional/case-hack.sh b/tests/functional/case-hack.sh
deleted file mode 100755
index fbc8242ff..000000000
--- a/tests/functional/case-hack.sh
+++ /dev/null
@@ -1,21 +0,0 @@
-#!/usr/bin/env bash
-
-source common.sh
-
-clearStore
-
-rm -rf $TEST_ROOT/case
-
-opts="--option use-case-hack true"
-
-# Check whether restoring and dumping a NAR that contains case
-# collisions is round-tripping, even on a case-insensitive system.
-nix-store $opts  --restore $TEST_ROOT/case < case.nar
-nix-store $opts --dump $TEST_ROOT/case > $TEST_ROOT/case.nar
-cmp case.nar $TEST_ROOT/case.nar
-[ "$(nix-hash $opts --type sha256 $TEST_ROOT/case)" = "$(nix-hash --flat --type sha256 case.nar)" ]
-
-# Check whether we detect true collisions (e.g. those remaining after
-# removal of the suffix).
-touch "$TEST_ROOT/case/xt_CONNMARK.h~nix~case~hack~3"
-(! nix-store $opts --dump $TEST_ROOT/case > /dev/null)
diff --git a/tests/functional/duplicate.nar b/tests/functional/duplicate.nar
new file mode 100644
index 000000000..1d0993ed4
Binary files /dev/null and b/tests/functional/duplicate.nar differ
diff --git a/tests/functional/local.mk b/tests/functional/local.mk
index b379eeefe..bdb47c2db 100644
--- a/tests/functional/local.mk
+++ b/tests/functional/local.mk
@@ -108,7 +108,7 @@ nix_tests = \
   derivation-json.sh \
   import-derivation.sh \
   nix_path.sh \
-  case-hack.sh \
+  nars.sh \
   placeholders.sh \
   ssh-relay.sh \
   build.sh \
diff --git a/tests/functional/nars.sh b/tests/functional/nars.sh
new file mode 100755
index 000000000..ba5a69bd2
--- /dev/null
+++ b/tests/functional/nars.sh
@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+clearStore
+
+# Check that NARs with duplicate directory entries are rejected.
+rm -rf "$TEST_ROOT/out"
+expectStderr 1 nix-store --restore "$TEST_ROOT/out" < duplicate.nar | grepQuiet "NAR directory is not sorted"
+
+# Check whether restoring and dumping a NAR that contains case
+# collisions is round-tripping, even on a case-insensitive system.
+rm -rf "$TEST_ROOT/case"
+opts=("--option" "use-case-hack" "true")
+nix-store "${opts[@]}" --restore "$TEST_ROOT/case" < case.nar
+nix-store "${opts[@]}" --dump "$TEST_ROOT/case" > "$TEST_ROOT/case.nar"
+cmp case.nar "$TEST_ROOT/case.nar"
+[ "$(nix-hash "${opts[@]}" --type sha256 "$TEST_ROOT/case")" = "$(nix-hash --flat --type sha256 case.nar)" ]
+
+# Check whether we detect true collisions (e.g. those remaining after
+# removal of the suffix).
+touch "$TEST_ROOT/case/xt_CONNMARK.h~nix~case~hack~3"
+(! nix-store $opts --dump $TEST_ROOT/case > /dev/null)