diff --git a/synthtool/sources/git.py b/synthtool/sources/git.py
index 55c3e2b61..d79165d2e 100644
--- a/synthtool/sources/git.py
+++ b/synthtool/sources/git.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import contextlib
+import fcntl
 import os
 import pathlib
 import re
@@ -44,6 +46,16 @@ def make_repo_clone_url(repo: str) -> str:
         return f"https://github.com/{repo}.git"
 
 
+@contextlib.contextmanager
+def file_lock(lock_path: pathlib.Path):
+    with open(lock_path, "w") as lock_f:
+        fcntl.flock(lock_f, fcntl.LOCK_EX)
+        try:
+            yield lock_f
+        finally:
+            fcntl.flock(lock_f, fcntl.LOCK_UN)
+
+
 def _local_default_branch(path: pathlib.Path) -> Union[str, None]:
     """Helper method to infer the default branch.
 
@@ -105,21 +117,33 @@ def clone(
 
         dest = dest / pathlib.Path(url).stem
 
-        if force and dest.exists():
-            shutil.rmtree(dest)
-
-        default_branch = None
-        if not dest.exists():
-            cmd = ["git", "clone", "--recurse-submodules", "--single-branch", url, dest]
-            shell.run(cmd, check=True)
-        else:
-            default_branch = _local_default_branch(dest)
-            shell.run(["git", "checkout", default_branch], cwd=str(dest), check=True)
-            shell.run(["git", "pull"], cwd=str(dest), check=True)
-        committish = committish or default_branch
-
-    if committish:
-        shell.run(["git", "reset", "--hard", committish], cwd=str(dest))
+    lock_file = dest.parent / (dest.name + ".lock")
+    with file_lock(lock_file):
+        if not preclone:
+            if force and dest.exists():
+                shutil.rmtree(dest)
+
+            default_branch = None
+            if not dest.exists():
+                cmd = [
+                    "git",
+                    "clone",
+                    "--recurse-submodules",
+                    "--single-branch",
+                    url,
+                    dest,
+                ]
+                shell.run(cmd, check=True)
+            else:
+                default_branch = _local_default_branch(dest)
+                shell.run(
+                    ["git", "checkout", default_branch], cwd=str(dest), check=True
+                )
+                shell.run(["git", "pull"], cwd=str(dest), check=True)
+            committish = committish or default_branch
+
+        if committish:
+            shell.run(["git", "reset", "--hard", committish], cwd=str(dest))
 
     # track all git repositories
     _tracked_paths.add(dest)
diff --git a/tests/test_git.py b/tests/test_git.py
index 0a1082ace..bafc23984 100644
--- a/tests/test_git.py
+++ b/tests/test_git.py
@@ -14,6 +14,7 @@
 
 import copy
 import importlib
+import fcntl
 import os
 import unittest
 from unittest import mock
@@ -87,6 +88,16 @@ def tearDown(self):
         os.environ = self.env
         return super().tearDown()
 
+    @mock.patch("fcntl.flock")
+    def testCloneConcurrencyPatch(self, mock_flock):
+        metadata.reset()
+        local_directory = git.clone("https://github.com/googleapis/nodejs-vision.git")
+        self.assertEqual("nodejs-vision", local_directory.name)
+        self.assertTrue(mock_flock.called)
+        # Should be called with LOCK_EX then LOCK_UN
+        mock_flock.assert_any_call(mock.ANY, fcntl.LOCK_EX)
+        mock_flock.assert_any_call(mock.ANY, fcntl.LOCK_UN)
+
     def testClone(self):
         # clear out metadata before creating new metadata and asserting on it
         metadata.reset()