diff --git a/swh/storage/tests/test_storage.py b/swh/storage/tests/test_storage.py
--- a/swh/storage/tests/test_storage.py
+++ b/swh/storage/tests/test_storage.py
@@ -6,7 +6,11 @@
 import copy
 import datetime
 import itertools
+import queue
 import random
+import sys
+import threading
+import time
 import unittest
 from collections import defaultdict
 from unittest.mock import Mock, patch
@@ -3971,6 +3975,59 @@
         self.assertEqual(missing, [self.cont['sha1']])
 
 
+@pytest.mark.db
+class TestStorageRaceConditions(TestStorageData, StorageTestDbFixture,
+                                unittest.TestCase):
+    def test_content_add_race(self):
+
+        results = queue.Queue()
+
+        def thread1():
+            db1 = None
+            try:
+                db1 = self.storage.get_db()
+                with db1.transaction() as cur1:
+                    ret = self.storage.content_add([self.cont], db=db1,
+                                                   cur=cur1)
+                results.put(('thread1', 'data', ret))
+            except Exception:
+                results.put(('thread1', 'exc', sys.exc_info()))
+            finally:
+                if db1:
+                    self.storage.put_db(db1)
+
+        def thread2():
+            db2 = None
+            try:
+                db2 = self.storage.get_db()
+                with db2.transaction() as cur2:
+                    ret = self.storage.content_add([self.cont], db=db2,
+                                                   cur=cur2)
+                results.put(('thread2', 'data', ret))
+            except Exception as e:
+                results.put(('thread2', 'exc', e))
+            finally:
+                if db2:
+                    self.storage.put_db(db2)
+
+        t1 = threading.Thread(target=thread1)
+        t2 = threading.Thread(target=thread2)
+        t1.start()
+        #time.sleep(1)
+        t2.start()
+        t1.join()
+        t2.join()
+
+        r1 = results.get(block=False)
+        r2 = results.get(block=False)
+
+        with pytest.raises(queue.Empty):
+            results.get(block=False)
+        assert {r1[0], r2[0]} == {'thread1', 'thread2'}
+        assert r1[1] == 'data', 'Got exception %r in %s' % (r1[2], r1[0])
+        assert r2[1] == 'data', 'Got exception %r in %s' % (r2[2], r2[0])
+
+
 @pytest.mark.db
 @pytest.mark.property_based
 class PropTestLocalStorage(CommonPropTestStorage, StorageTestDbFixture,