diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -33,7 +33,10 @@
 from .exc import StorageArgumentException, StorageDBError
 from .algos import diff
 from .metrics import timed, send_metric, process_metrics
-from .utils import get_partition_bounds_bytes
+from .utils import (
+    get_partition_bounds_bytes, extract_collision_hash,
+    content_to_primary_key
+)
 from .writer import JournalWriter
 
 
@@ -158,14 +161,27 @@
         except psycopg2.IntegrityError as e:
             if e.diag.sqlstate == '23505' and \
                     e.diag.table_name == 'content':
-                constraint_to_hash_name = {
-                    'content_pkey': 'sha1',
-                    'content_sha1_git_idx': 'sha1_git',
-                    'content_sha256_idx': 'sha256',
+                message_detail = e.diag.message_detail
+                if message_detail:
+                    hash_name, hash_id = extract_collision_hash(message_detail)
+                    collision_contents_hashes_as_tuple = [
+                        content_to_primary_key(c) for c in content
+                        if getattr(c, hash_name) == hash_id
+                    ]
+                else:
+                    constraint_to_hash_name = {
+                        'content_pkey': 'sha1',
+                        'content_sha1_git_idx': 'sha1_git',
+                        'content_sha256_idx': 'sha256',
                     }
-                colliding_hash_name = constraint_to_hash_name \
-                    .get(e.diag.constraint_name)
-                raise HashCollision(colliding_hash_name) from None
+                    hash_name = constraint_to_hash_name \
+                        .get(e.diag.constraint_name)
+                    hash_id = None
+                    collision_contents_hashes_as_tuple = None
+
+                raise HashCollision(
+                    hash_name, hash_id, collision_contents_hashes_as_tuple
+                ) from None
             else:
                 raise
 
diff --git a/swh/storage/tests/test_utils.py b/swh/storage/tests/test_utils.py
new file mode 100644
--- /dev/null
+++ b/swh/storage/tests/test_utils.py
@@ -0,0 +1,54 @@
+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from swh.model.hashutil import hash_to_bytes, DEFAULT_ALGORITHMS
+from swh.model.model import Content
+from swh.storage.utils import extract_collision_hash, content_to_primary_key
+
+from .storage_data import data
+
+
+def test_extract_collision_hash():
+    for msg, expected_result in [
+            (
+                'Key (sha1)=(\\x34973274ccef6ab4dfaaf86599792fa9c3fe4689) ...',
+                ('sha1', hash_to_bytes(
+                    '34973274ccef6ab4dfaaf86599792fa9c3fe4689')),
+            ),
+            (
+                'Key (sha1_git)=(\\x34973274ccef6ab4dfaaf86599792fa9c3fe4699) already exists',  # noqa
+                ('sha1_git', hash_to_bytes(
+                    '34973274ccef6ab4dfaaf86599792fa9c3fe4699')),
+            ),
+            (
+                'Key (sha256)=(\\x673650f936cb3b0a2f93ce09d81be10748b1b203c19e8176b4eefc1964a0cf3a) ...',  # noqa
+                ('sha256', hash_to_bytes(
+                    '673650f936cb3b0a2f93ce09d81be10748b1b203c19e8176b4eefc1964a0cf3a'))  # noqa
+            ),
+            (
+                'Key (blake2s)=(\\xd5fe1939576527e42cfd76a9455a2432fe7f56669564577dd93c4280e76d661d) ...',  # noqa
+                ('blake2s', hash_to_bytes(
+                    'd5fe1939576527e42cfd76a9455a2432fe7f56669564577dd93c4280e76d661d'))  # noqa
+            ),
+    ]:
+        assert extract_collision_hash(msg) == expected_result
+
+    assert extract_collision_hash('Nothing matching') is None
+
+
+def test_content_to_primary_key():
+    """Convert contents into a tuple of signatures
+
+    """
+    for content_dict in [data.cont, data.cont2, data.cont3]:
+        c = Content.from_dict(content_dict)
+        expected_hashes = c.hashes()
+
+        actual_pk = content_to_primary_key(c)
+
+        assert len(actual_pk) == len(DEFAULT_ALGORITHMS)
+        for algo, actual_hash in actual_pk:
+            assert algo in DEFAULT_ALGORITHMS
+            assert actual_hash == expected_hashes[algo]
diff --git a/swh/storage/utils.py b/swh/storage/utils.py
--- a/swh/storage/utils.py
+++ b/swh/storage/utils.py
@@ -1,9 +1,14 @@
-# Copyright (C) 2019  The Software Heritage developers
+# Copyright (C) 2019-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
-from typing import Optional, Tuple
+import re
+
+from typing import List, Optional, Tuple
+
+from swh.model.hashutil import hash_to_bytes, DEFAULT_ALGORITHMS
+from swh.model.model import Content
 
 
 def _is_power_of_two(n: int) -> bool:
@@ -40,3 +45,44 @@
     end = None if i == n-1 \
         else (partition_size*(i+1)).to_bytes(nb_bytes, 'big')
     return (start, end)
+
+
+def extract_collision_hash(error_message: str) -> Optional[Tuple[str, bytes]]:
+    """Utilities to extract the hash information from a hash collision error.
+
+    Hash collision error message are of the form:
+    'Key (<hash-type>)=(<double-escaped-hash) already exists.'
+
+    for example:
+    'Key (sha1)=(\\x34973274ccef6ab4dfaaf86599792fa9c3fe4689) already exists.'
+
+    Return:
+        A formatted string
+
+    """
+    pattern = r'\w* \((?P<type>[a-z0-9_]+)\)=\((?P<id>[\\a-f0-9x]+)\) \w*'
+    result = re.match(pattern, error_message)
+    if result:
+        hash_type = result.group('type')
+        hash_id = result.group('id').replace('\\x', '')
+        return hash_type, hash_to_bytes(hash_id)
+    return None
+
+
+def content_to_primary_key(content: Content) -> List[
+        Tuple[str, bytes]
+]:
+    """Convert a content to its primary key representation.
+
+    Args:
+        content: Content object
+
+    Returns
+        a tuple representing its primary key
+
+    """
+    primary_key = []
+    for algo in DEFAULT_ALGORITHMS:
+        tuple_key: Tuple[str, bytes] = (algo, getattr(content, algo))
+        primary_key.append(tuple_key)
+    return primary_key