diff --git i/lix/libexpr/primops/fetchTree.cc w/lix/libexpr/primops/fetchTree.cc
index 93b08ecc9..6d04ce24b 100644
--- i/lix/libexpr/primops/fetchTree.cc
+++ w/lix/libexpr/primops/fetchTree.cc
@@ -168,6 +168,11 @@ static void fetchTree(
                     "attribute 'name' isn’t supported in call to 'fetchTree'"
                 ).atPos(pos).debugThrow();
 
+        // HACK: When using `fetchGit`, locking with only the hash should happen
+        //       as we don't care about flake hallucinations about `lastModified`
+        if (type == "git" && attrs.contains("narHash"))
+            attrs["type"] = "git-locked";
+
         input = fetchers::Input::fromAttrs(std::move(attrs));
     } else {
         auto url = state.coerceToString(pos, *args[0], context,
diff --git i/lix/libfetchers/builtin-fetchers.hh w/lix/libfetchers/builtin-fetchers.hh
index d3be7f7f2..d1389b8ba 100644
--- i/lix/libfetchers/builtin-fetchers.hh
+++ w/lix/libfetchers/builtin-fetchers.hh
@@ -10,6 +10,7 @@ std::unique_ptr<InputScheme> makePathInputScheme();
 std::unique_ptr<InputScheme> makeFileInputScheme();
 std::unique_ptr<InputScheme> makeTarballInputScheme();
 std::unique_ptr<InputScheme> makeGitInputScheme();
+std::unique_ptr<InputScheme> makeGitLockedInputScheme();
 std::unique_ptr<InputScheme> makeMercurialInputScheme();
 std::unique_ptr<InputScheme> makeGitHubInputScheme();
 std::unique_ptr<InputScheme> makeGitLabInputScheme();
diff --git i/lix/libfetchers/fetchers.cc w/lix/libfetchers/fetchers.cc
index 0dc9f5e0c..91cd9332d 100644
--- i/lix/libfetchers/fetchers.cc
+++ w/lix/libfetchers/fetchers.cc
@@ -22,6 +22,7 @@ void initLibFetchers()
     registerInputScheme(makeTarballInputScheme());
     registerInputScheme(makeFileInputScheme());
     registerInputScheme(makeGitInputScheme());
+    registerInputScheme(makeGitLockedInputScheme());
     registerInputScheme(makeMercurialInputScheme());
     registerInputScheme(makeGitHubInputScheme());
     registerInputScheme(makeGitLabInputScheme());
diff --git i/lix/libfetchers/git.cc w/lix/libfetchers/git.cc
index 21fa1904d..f9573eacd 100644
--- i/lix/libfetchers/git.cc
+++ w/lix/libfetchers/git.cc
@@ -812,4 +812,40 @@ std::unique_ptr<InputScheme> makeGitInputScheme()
     return std::make_unique<GitInputScheme>();
 }
 
+struct GitLockedInputScheme : GitInputScheme {
+
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
+    {
+        if (maybeGetStrAttr(attrs, "type") != "git-locked") return {};
+
+        for (auto & [name, value] : attrs)
+            if (name != "type" && name != "url" && name != "ref" && name != "rev" && name != "shallow" && name != "submodules" && name != "lastModified" && name != "revCount" && name != "narHash" && name != "allRefs" && name != "name" && name != "dirtyRev" && name != "dirtyShortRev")
+                throw Error("unsupported Git input attribute '%s'", name);
+
+        parseURL(getStrAttr(attrs, "url"));
+        maybeGetBoolAttr(attrs, "shallow");
+        maybeGetBoolAttr(attrs, "submodules");
+        maybeGetBoolAttr(attrs, "allRefs");
+
+        if (auto ref = maybeGetStrAttr(attrs, "ref")) {
+            if (std::regex_search(*ref, badGitRefRegex))
+                throw BadURL("invalid Git branch/tag name '%s'", *ref);
+        }
+
+        Input input;
+        input.attrs = attrs;
+        return input;
+    }
+
+    bool hasAllInfo(const Input & input) const override {
+        return true;
+    }
+
+};
+
+std::unique_ptr<InputScheme> makeGitLockedInputScheme()
+{
+    return std::make_unique<GitLockedInputScheme>();
+}
+
 }