diff --git a/pkgs/development/compilers/llvm/update-git.py b/pkgs/development/compilers/llvm/update-git.py
index 880cad1c72b..488f415f439 100755
--- a/pkgs/development/compilers/llvm/update-git.py
+++ b/pkgs/development/compilers/llvm/update-git.py
@@ -79,8 +79,14 @@ hash = nix_prefetch_url(f'https://github.com/llvm/llvm-project/archive/{commit["
 print('Updating default.nix...')
 with fileinput.FileInput(DEFAULT_NIX, inplace=True) as f:
     for line in f:
+        if match := re.search(r'^  rev-version = "unstable-(.+)";', line):
+                old_date = match.group(1)
         result = re.sub(r'^  release_version = ".+";', f'  release_version = "{release_version}";', line)
         result = re.sub(r'^  rev = ".*";', f'  rev = "{commit["sha"]}";', result)
         result = re.sub(r'^  rev-version = ".+";', f'  rev-version = "{version}";', result)
         result = re.sub(r'^    sha256 = ".+";', f'    sha256 = "{hash}";', result)
         print(result, end='')
+# Commit the result:
+commit_message = f"llvmPackages_git: {old_date} -> {date}"
+subprocess.run(['git', 'add', DEFAULT_NIX], check=True)
+subprocess.run(['git', 'commit', '--file=-'], input=commit_message.encode(), check=True)