diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 225483804..cca89d847 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -270,7 +270,13 @@ static Generator<Entry> parseObject(Source & source, const Path & path)
                 co_yield MetadataString{name};
                 if (name.empty() || name == "." || name == ".."
                     || name.find('/') != std::string::npos
-                    || name.find((char) 0) != std::string::npos)
+                    || name.find((char) 0) != std::string::npos
+                    // The case hack is a thing that only exists on the
+                    // filesystem.
+                    // Unpacking one appearing in a NAR is super
+                    // sketchy because it will at minimum cause corruption at
+                    // the time of repacking the NAR.
+                    || name.find(caseHackSuffix) != std::string::npos)
                 {
                     throw Error("NAR contains invalid file name '%1%'", name);
                 }
diff --git a/tests/functional2/store/test_evil_nars.py b/tests/functional2/store/test_evil_nars.py
index d658a15f3..937eed0ce 100644
--- a/tests/functional2/store/test_evil_nars.py
+++ b/tests/functional2/store/test_evil_nars.py
@@ -60,15 +60,14 @@ EVIL_NARS: list[tuple[str, NarItem]] = [
             (b'meow', Regular(False, b'kbityy'))
         ])),
     ])),
-    # FIXME: ban casehacked filenames being extracted from NARs
-    # ('invalid-casehack-1', Directory([
-    #     (b'ZZZ~nix~case~hack~2', Regular(False, b'meow')),
-    #     (b'zzz~nix~case~hack~1', Regular(False, b'eepy')),
-    # ])),
-    # ('invalid-casehack-2', Directory([
-    #     (b'ZZZ~nix~case~hack~1', Regular(False, b'meow')),
-    #     (b'zzz~nix~case~hack~1', Regular(False, b'eepy')),
-    # ])),
+    ('invalid-casehack-1', Directory([
+        (b'ZZZ~nix~case~hack~2', Regular(False, b'meow')),
+        (b'zzz~nix~case~hack~1', Regular(False, b'eepy')),
+    ])),
+    ('invalid-casehack-2', Directory([
+        (b'ZZZ~nix~case~hack~1', Regular(False, b'meow')),
+        (b'zzz~nix~case~hack~1', Regular(False, b'eepy')),
+    ])),
 ]
 
 @pytest.mark.parametrize(['name', 'nar'], EVIL_NARS)