diff --git a/src/libfetchers/git-lfs-fetch.hh b/src/libfetchers/git-lfs-fetch.hh
index 3946dac05..84cc056fa 100644
--- a/src/libfetchers/git-lfs-fetch.hh
+++ b/src/libfetchers/git-lfs-fetch.hh
@@ -117,7 +117,7 @@ struct Fetch {
 
   void init(git_repository* repo, const std::string& gitattributesContent);
   bool hasAttribute(const std::string& path, const std::string& attrName, const std::string& attrValue) const;
-  void fetch(const std::string& pointerFileContents, const std::string& pointerFilePath, Sink& sink) const;
+  void fetch(const git_blob* pointerBlob, const std::string& pointerFilePath, Sink& sink) const;
   std::vector<nlohmann::json> fetchUrls(const std::vector<Md> &metadatas) const;
 };
 
@@ -185,8 +185,6 @@ void downloadToSink(const std::string &url, const std::string &authHeader, Sink
 }
 
 
-
-
 std::string getLfsApiToken(const GitUrl& u) {
   const auto [maybeUserAndHost, path] = u.toSsh();
   auto [status, output] = runProgram(RunOptions {
@@ -216,7 +214,6 @@ std::string getLfsEndpointUrl(git_repository *repo) {
       return "";
   }
 
-
   const char *url_c_str = git_remote_url(remote);
   if (!url_c_str) {
     return "";
@@ -241,35 +238,60 @@ std::string git_attr_value_to_string(git_attr_value_t value) {
 }
 
 
-Md parseLfsMetadata(const std::string &content, const std::string &filename) {
+std::optional<Md> parseLfsMetadata(const std::string &content, const std::string &filename) {
+  // https://github.com/git-lfs/git-lfs/blob/2ef4108/docs/spec.md
+  //
   // example git-lfs pointer file:
   // version https://git-lfs.github.com/spec/v1
   // oid sha256:f5e02aa71e67f41d79023a128ca35bad86cf7b6656967bfe0884b3a3c4325eaf
   // size 10000000
-  std::istringstream iss(content);
-  std::string line;
-  std::string oid;
-  size_t size = 0;
+  // (ending \n)
 
-  while (getline(iss, line)) {
-    std::size_t pos = line.find("oid sha256:");
-    if (pos != std::string::npos) {
-      oid = line.substr(pos + 11); // skip "oid sha256:"
-      continue;
-    }
-
-    pos = line.find("size ");
-    if (pos != std::string::npos) {
-      std::string sizeStr =
-          line.substr(pos + 5); // skip "size "
-      size = std::stol(sizeStr);
-      continue;
-    }
+  if (!content.starts_with("version ")) {
+    // Invalid pointer file
+    return std::nullopt;
   }
 
-  return Md{filename, oid, size};
-}
+  if (!content.starts_with("version https://git-lfs.github.com/spec/v1")) {
+    // In case there's new spec versions in the future, but for now only v1 exists
+    debug("Invalid version found on potential lfs pointer file, skipping");
+    return std::nullopt;
+  }
 
+  std::istringstream iss(content);
+  std::string line;
+
+  std::string oid;
+  std::string size;
+
+  while (getline(iss, line)) {
+    if (line.starts_with("version ")) {
+      continue;
+    }
+    if (line.starts_with("oid sha256:")) {
+      oid = line.substr(11); // skip "oid sha256:"
+      continue;
+    }
+    if (line.starts_with("size ")) {
+      size = line.substr(5); // skip "size "
+      continue;
+    }
+
+    debug("Custom extension '%s' found, ignoring", line);
+  }
+
+  if (oid.length() != 64 || !std::all_of(oid.begin(), oid.end(), ::isxdigit)) {
+    debug("Invalid sha256 %s, skipping", oid);
+    return std::nullopt;
+  }
+
+  if (size.length() == 0 || !std::all_of(size.begin(), size.end(), ::isdigit)) {
+    debug("Invalid size %s, skipping", size);
+    return std::nullopt;
+  }
+
+  return std::make_optional(Md{filename, oid, std::stoul(size)});
+}
 
 
 // there's already a ParseURL here https://github.com/b-camacho/nix/blob/ef6fa54e05cd4134ec41b0d64c1a16db46237f83/src/libutil/url.cc#L13
@@ -386,7 +408,6 @@ void Fetch::init(git_repository* repo, const std::string& gitattributesContent)
 }
 
 
-
 bool Fetch::hasAttribute(const std::string& path, const std::string& attrName, const std::string& attrValue) const
 {
     for (auto it = rules.rbegin(); it != rules.rend(); ++it) {
@@ -481,10 +502,32 @@ std::vector<nlohmann::json> Fetch::fetchUrls(const std::vector<Md> &metadatas) c
   }
 }
 
-void Fetch::fetch(const std::string& pointerFileContents, const std::string& pointerFilePath, Sink& sink) const {
+void Fetch::fetch(const git_blob* pointerBlob, const std::string& pointerFilePath, Sink& sink) const {
+  constexpr size_t chunkSize = 128 * 1024; // 128 KiB
+  auto size = git_blob_rawsize(pointerBlob);
+
+  if (size >= 1024) {
+    debug("Skip git-lfs, pointer file too large");
+    warn("Encountered a file that should have been a pointer, but wasn't: %s", pointerFilePath);
+    for (size_t offset = 0; offset < size; offset += chunkSize) {
+        sink(std::string((const char *) git_blob_rawcontent(pointerBlob) + offset, std::min(chunkSize, size - offset)));
+    }
+    return;
+  }
+
+  const auto pointerFileContents = std::string((const char *) git_blob_rawcontent(pointerBlob), size);
   const auto md = parseLfsMetadata(std::string(pointerFileContents), std::string(pointerFilePath));
+  if (md == std::nullopt) {
+    debug("Skip git-lfs, invalid pointer file");
+    warn("Encountered a file that should have been a pointer, but wasn't: %s", pointerFilePath);
+    for (size_t offset = 0; offset < size; offset += chunkSize) {
+        sink(std::string((const char *) git_blob_rawcontent(pointerBlob) + offset, std::min(chunkSize, size - offset)));
+    }
+    return;
+  }
+
   std::vector<Md> vMds;
-  vMds.push_back(md);
+  vMds.push_back(md.value());
   const auto objUrls = fetchUrls(vMds);
 
   const auto obj = objUrls[0];
@@ -507,4 +550,3 @@ void Fetch::fetch(const std::string& pointerFileContents, const std::string& poi
 } // namespace lfs
 
 } // namespace nix
-
diff --git a/src/libfetchers/git-utils.cc b/src/libfetchers/git-utils.cc
index dc8086a2c..073e3fcad 100644
--- a/src/libfetchers/git-utils.cc
+++ b/src/libfetchers/git-utils.cc
@@ -676,29 +676,31 @@ struct GitSourceAccessor : SourceAccessor
         , root(peelToTreeOrBlob(lookupObject(*repo, hashToOID(rev)).get()))
         , lfsFetch(lfsFetch)
     {
+        if (lfsFetch && !lookup(CanonPath(".gitattributes"))) {
+            warn("Requested to fetch lfs files, but no .gitattributes file was found, ignoring");
+        }
     }
 
     std::string readBlob(const CanonPath & path, bool symlink)
     {
         const auto blob = getBlob(path, symlink);
 
-        const auto data = std::string((const char *) git_blob_rawcontent(blob.get()), git_blob_rawsize(blob.get()));
-
-        if (path != CanonPath(".gitattributes") && lfsFetch) {
+        if (lfsFetch && path != CanonPath(".gitattributes") && lookup(CanonPath(".gitattributes"))) {
             auto& _lfsFetch = *lfsFetch;
             if (!_lfsFetch.ready) {
                 const auto contents = readFile(CanonPath(".gitattributes"));
                 _lfsFetch.init(*repo, contents);
-                };
+            }
+
             auto pathStr = std::string(path.rel());
             if (_lfsFetch.hasAttribute(pathStr, "filter", "lfs")) {
                 StringSink s;
-                _lfsFetch.fetch(data, pathStr, s);
+                _lfsFetch.fetch(blob.get(), pathStr, s);
                 return s.s;
             }
         }
 
-        return data;
+        return std::string((const char *) git_blob_rawcontent(blob.get()), git_blob_rawsize(blob.get()));
     }
 
     void readFile(
@@ -709,11 +711,7 @@ struct GitSourceAccessor : SourceAccessor
         auto size = git_blob_rawsize(blob.get());
         sizeCallback(size);
 
-        // if lfs, this is just a pointer file
-        // if not lfs then it's not big either way
-        auto contents = std::string((const char *) git_blob_rawcontent(blob.get()), size);
-
-        if (lfsFetch && path != CanonPath(".gitattributes")) {
+        if (lfsFetch && path != CanonPath(".gitattributes") && lookup(CanonPath(".gitattributes"))) {
             auto& _lfsFetch = *lfsFetch;
             if (!_lfsFetch.ready) {
                 const auto contents = readFile(CanonPath(".gitattributes"));
@@ -722,13 +720,15 @@ struct GitSourceAccessor : SourceAccessor
 
             auto pathStr = std::string(path.rel());
             if (_lfsFetch.hasAttribute(pathStr, "filter", "lfs")) {
-                _lfsFetch.fetch(contents, pathStr, sink);
+                _lfsFetch.fetch(blob.get(), pathStr, sink);
                 return;
             }
         }
 
-        // either not using lfs or file should not be smudged
-        sink(contents);
+        constexpr size_t chunkSize = 128 * 1024; // 128 KiB
+        for (size_t offset = 0; offset < size; offset += chunkSize) {
+            sink(std::string((const char *) git_blob_rawcontent(blob.get()) + offset, std::min(chunkSize, size - offset)));
+        }
     }
 
     std::string readFile(const CanonPath & path) override
diff --git a/tests/nixos/fetch-git/test-cases/lfs/default.nix b/tests/nixos/fetch-git/test-cases/lfs/default.nix
index e414a8018..a339cea91 100644
--- a/tests/nixos/fetch-git/test-cases/lfs/default.nix
+++ b/tests/nixos/fetch-git/test-cases/lfs/default.nix
@@ -1,72 +1,179 @@
 {
   # mostly copied from https://github.com/NixOS/nix/blob/358c26fd13a902d9a4032a00e6683571be07a384/tests/nixos/fetch-git/test-cases/fetchTree-shallow/default.nix#L1
   # ty @DavHau
-  description = "fetchGit smudges LFS pointers iff lfs=true";
+  description = "fetchGit smudges LFS pointers if lfs=true";
   script = ''
+    expected_max_size_lfs_pointer = 1024 # 1 KiB (values >= than this cannot be pointers, and test files are >= 1 MiB)
+
     # purge nix git cache to make sure we start with a clean slate
     client.succeed("rm -rf ~/.cache/nix")
 
-    # add an lfs-enrolled file to the repo:
-    client.succeed(f"dd if=/dev/urandom of={repo.path}/beeg bs=1M count=1")
-    client.succeed(f"{repo.git} lfs install")
-    client.succeed(f"{repo.git} lfs track --filename \"beeg\"")
-    client.succeed(f"{repo.git} add .gitattributes")
-    client.succeed(f"{repo.git} add beeg")
-    client.succeed(f"{repo.git} commit -m 'commit1'")
-    client.succeed(f"{repo.git} push origin main")
 
-    # memoize the revision
-    commit1_rev = client.succeed(f"""
-      {repo.git} rev-parse HEAD
-    """).strip()
+    # Request lfs fetch without any .gitattributes file
+    ############################################################################
+
+    client.succeed(f"dd if=/dev/urandom of={repo.path}/regular bs=1M count=1 >&2")
+    client.succeed(f"{repo.git} add : >&2")
+    client.succeed(f"{repo.git} commit -m 'no .gitattributes' >&2")
+    client.succeed(f"{repo.git} push origin main >&2")
+
+    # memorize the revision
+    no_gitattributes_rev = client.succeed(f"{repo.git} rev-parse HEAD").strip()
+
+    # fetch with lfs=true, and check that the lack of .gitattributes does not break anything
+    fetchGit_no_gitattributes_expr = f"""
+      builtins.fetchGit {{
+        url = "{repo.remote}";
+        rev = "{no_gitattributes_rev}";
+        ref = "main";
+        lfs = true;
+      }}
+    """
+    fetched_no_gitattributes = client.succeed(f"""
+      nix eval --impure --raw --expr '({fetchGit_no_gitattributes_expr}).outPath'
+    """)
+    client.succeed(f"cmp {repo.path}/regular {fetched_no_gitattributes}/regular >&2")
+
+
+    # Add a file that should be tracked by lfs, but isn't
+    # (git lfs cli only throws a warning "Encountered 1 file that should have
+    # been a pointer, but wasn't")
+    ############################################################################
+
+    client.succeed(f"dd if=/dev/urandom of={repo.path}/black_sheep bs=1M count=1 >&2")
+    client.succeed(f"echo 'black_sheep filter=lfs -text' >>{repo.path}/.gitattributes")
+    client.succeed(f"{repo.git} add : >&2")
+    client.succeed(f"{repo.git} commit -m 'add misleading file' >&2")
+    client.succeed(f"{repo.git} push origin main >&2")
+
+    # memorize the revision
+    bad_lfs_rev = client.succeed(f"{repo.git} rev-parse HEAD").strip()
+
+    # prove that it can be cloned with regular git first
+    # (here we see the warning as stated above)
+    from tempfile import TemporaryDirectory
+    with TemporaryDirectory() as tempdir:
+      client.succeed(f"git clone -n {repo.remote} {tempdir} >&2")
+      client.succeed(f"git -C {tempdir} lfs install >&2")
+      client.succeed(f"git -C {tempdir} checkout {bad_lfs_rev} >&2")
+
+      # check that the file is not a pointer, as expected
+      file_size_git = client.succeed(f"stat -c %s {tempdir}/black_sheep").strip()
+      assert int(file_size_git) >= expected_max_size_lfs_pointer, \
+        f"non lfs file is {file_size_git}b (<{expected_max_size_lfs_pointer}b), probably a test implementation error"
+
+      lfs_files = client.succeed(f"git -C {tempdir} lfs ls-files").strip()
+      assert lfs_files == "", "non lfs file is tracked by lfs, probably a test implementation error"
+
+      client.succeed(f"cmp {repo.path}/black_sheep {tempdir}/black_sheep >&2")
+
+    # now fetch without lfs, check that the file is not a pointer
+    fetchGit_bad_lfs_without_lfs_expr = f"""
+      builtins.fetchGit {{
+        url = "{repo.remote}";
+        rev = "{bad_lfs_rev}";
+        ref = "main";
+        lfs = false;
+      }}
+    """
+    fetched_bad_lfs_without_lfs = client.succeed(f"""
+      nix eval --impure --raw --expr '({fetchGit_bad_lfs_without_lfs_expr}).outPath'
+    """)
+
+    # check that file was not somehow turned into a pointer
+    file_size_bad_lfs_without_lfs = client.succeed(f"stat -c %s {fetched_bad_lfs_without_lfs}/black_sheep").strip()
+
+    assert int(file_size_bad_lfs_without_lfs) >= expected_max_size_lfs_pointer, \
+      f"non lfs-enrolled file is {file_size_bad_lfs_without_lfs}b (<{expected_max_size_lfs_pointer}b), probably a test implementation error"
+    client.succeed(f"cmp {repo.path}/black_sheep {fetched_bad_lfs_without_lfs}/black_sheep >&2")
+
+    # finally fetch with lfs=true, and check that the bad file does not break anything
+    fetchGit_bad_lfs_with_lfs_expr = f"""
+      builtins.fetchGit {{
+        url = "{repo.remote}";
+        rev = "{bad_lfs_rev}";
+        ref = "main";
+        lfs = true;
+      }}
+    """
+    fetchGit_bad_lfs_with_lfs = client.succeed(f"""
+      nix eval --impure --raw --expr '({fetchGit_bad_lfs_with_lfs_expr}).outPath'
+    """)
+
+    client.succeed(f"cmp {repo.path}/black_sheep {fetchGit_bad_lfs_with_lfs}/black_sheep >&2")
+
+
+    # Add an lfs-enrolled file to the repo
+    ############################################################################
+
+    client.succeed(f"dd if=/dev/urandom of={repo.path}/beeg bs=1M count=1 >&2")
+    client.succeed(f"{repo.git} lfs install >&2")
+    client.succeed(f"{repo.git} lfs track --filename beeg >&2")
+    client.succeed(f"{repo.git} add : >&2")
+    client.succeed(f"{repo.git} commit -m 'add lfs file' >&2")
+    client.succeed(f"{repo.git} push origin main >&2")
+
+    # memorize the revision
+    lfs_file_rev = client.succeed(f"{repo.git} rev-parse HEAD").strip()
 
     # first fetch without lfs, check that we did not smudge the file
     fetchGit_nolfs_expr = f"""
       builtins.fetchGit {{
         url = "{repo.remote}";
-        rev = "{commit1_rev}";
+        rev = "{lfs_file_rev}";
         ref = "main";
         lfs = false;
       }}
     """
-
-    # fetch the repo via nix
     fetched_nolfs = client.succeed(f"""
       nix eval --impure --raw --expr '({fetchGit_nolfs_expr}).outPath'
     """)
 
     # check that file was not smudged
-    file_size_nolfs = client.succeed(f"""
-      stat -c %s {fetched_nolfs}/beeg
-    """).strip()
+    file_size_nolfs = client.succeed(f"stat -c %s {fetched_nolfs}/beeg").strip()
 
-    expected_max_size_lfs = 1024
-    assert int(file_size_nolfs) < expected_max_size_lfs, f"did not set lfs=true, yet lfs-enrolled file is {file_size_nolfs}b (>{expected_max_size_lfs}b), probably smudged when we should not have"
+    assert int(file_size_nolfs) < expected_max_size_lfs_pointer, \
+      f"did not set lfs=true, yet lfs-enrolled file is {file_size_nolfs}b (>{expected_max_size_lfs_pointer}b), probably smudged when we should not have"
 
     # now fetch with lfs=true and check that the file was smudged
     fetchGit_lfs_expr = f"""
       builtins.fetchGit {{
         url = "{repo.remote}";
-        rev = "{commit1_rev}";
+        rev = "{lfs_file_rev}";
         ref = "main";
         lfs = true;
       }}
     """
-
-
-    # fetch the repo via nix
     fetched_lfs = client.succeed(f"""
       nix eval --impure --raw --expr '({fetchGit_lfs_expr}).outPath'
     """)
 
-    assert fetched_lfs != fetched_nolfs, f"fetching with and without lfs yielded the same store path {fetched_lfs}, fingerprinting error?"
+    assert fetched_lfs != fetched_nolfs, \
+      f"fetching with and without lfs yielded the same store path {fetched_lfs}, fingerprinting error?"
 
     # check that file was smudged
-    file_size_lfs = client.succeed(f"""
-      stat -c %s {fetched_lfs}/beeg
-    """).strip()
+    file_size_lfs = client.succeed(f"stat -c %s {fetched_lfs}/beeg").strip()
+    assert int(file_size_lfs) >= expected_max_size_lfs_pointer, \
+      f"set lfs=true, yet lfs-enrolled file is {file_size_lfs}b (<{expected_max_size_lfs_pointer}), probably did not smudge when we should have"
 
-    expected_min_size_lfs = 1024 * 1024  # 1MB
-    assert int(file_size_lfs) >= expected_min_size_lfs, f"set lfs=true, yet lfs-enrolled file is {file_size_lfs}b (<{expected_min_size_lfs}), probably did not smudge when we should have"
+
+    # Check that default is lfs=false
+    ############################################################################
+    fetchGit_default_expr = f"""
+      builtins.fetchGit {{
+        url = "{repo.remote}";
+        rev = "{lfs_file_rev}";
+        ref = "main";
+      }}
+    """
+    fetched_default = client.succeed(f"""
+      nix eval --impure --raw --expr '({fetchGit_default_expr}).outPath'
+    """)
+
+    # check that file was not smudged
+    file_size_default = client.succeed(f"stat -c %s {fetched_default}/beeg").strip()
+
+    assert int(file_size_default) < expected_max_size_lfs_pointer, \
+      f"did not set lfs, yet lfs-enrolled file is {file_size_default}b (>{expected_max_size_lfs_pointer}b), probably bad default value"
   '';
 }