diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3bdbb9a..476d7b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.0.4] - 2026-06-13
+
+### Fixed
+
+- `upsert_and_log` (and other `*_and_log`) no longer raise `Ecto.ConstraintError` on `audit_log_pkey` under concurrent upserts. `changelog_changeset` now declares `unique_constraint(:id, name: "<table>_pkey")` so Ecto turns the violation into a changeset error that the logging paths swallow. Closes OPS-4571.
+
 ## [1.0.3] - 2026-05-28
 
 ### Fixed
diff --git a/lib/ecto_trail/ecto_trail.ex b/lib/ecto_trail/ecto_trail.ex
index 74d7075..ecdd2cf 100644
--- a/lib/ecto_trail/ecto_trail.ex
+++ b/lib/ecto_trail/ecto_trail.ex
@@ -55,6 +55,8 @@ defmodule EctoTrail do
   @default_max_params 65_000
   @changelog_fields [:actor_id, :resource, :resource_id, :changeset, :change_type]
   @not_loaded_pattern "Ecto.Association.NotLoaded"
+  @audit_log_table Application.compile_env(:ecto_trail, :table_name, "audit_log")
+  @audit_log_pkey "#{@audit_log_table}_pkey"
 
   defmacro __using__(_) do
     quote do
@@ -572,6 +574,8 @@ defmodule EctoTrail do
   defp map_custom_ecto_type(value), do: value
 
   defp changelog_changeset(attrs) do
-    Changeset.cast(%Changelog{}, attrs, @changelog_fields)
+    %Changelog{}
+    |> Changeset.cast(attrs, @changelog_fields)
+    |> Changeset.unique_constraint(:id, name: @audit_log_pkey)
   end
 end
diff --git a/mix.exs b/mix.exs
index c895a54..e08c811 100644
--- a/mix.exs
+++ b/mix.exs
@@ -1,7 +1,7 @@
 defmodule EctoTrail.Mixfile do
   use Mix.Project
 
-  @version "1.0.3"
+  @version "1.0.4"
 
   def project do
     [
diff --git a/test/unit/ecto_trail_test.exs b/test/unit/ecto_trail_test.exs
index 1a44768..5c92dd8 100644
--- a/test/unit/ecto_trail_test.exs
+++ b/test/unit/ecto_trail_test.exs
@@ -225,6 +225,35 @@ defmodule EctoTrailTest do
                change_type: :upsert
              } = TestRepo.one(Changelog)
     end
+
+    test "upsert_and_log does not raise Ecto.ConstraintError on audit_log pkey collision (concurrent upsert case)" do
+      {:ok, schema} = TestRepo.insert(%Resource{name: "uq-base"})
+
+      # Seed one audit row so the pkey sequence exists and has a value, then rewind it
+      # so the *next* autogenerated PK will collide (serial id in test DB).
+      {:ok, _seed} =
+        TestRepo.insert(%Changelog{
+          actor_id: "seed",
+          resource: "resources",
+          resource_id: "999",
+          changeset: %{},
+          change_type: :insert
+        })
+
+      max_id = TestRepo.one(from(c in Changelog, select: max(c.id)))
+      seq_name = "audit_log_id_seq"
+      Ecto.Adapters.SQL.query!(TestRepo, "SELECT setval($1, $2, true)", [seq_name, max_id - 1])
+
+      # Before the fix this raises Ecto.ConstraintError because log_changes did a bare insert
+      # without unique_constraint(:id, name: "audit_log_pkey"). After fix the violation becomes
+      # a normal {:error, changeset} which the *_and_log paths swallow (audit is best-effort).
+      result =
+        schema
+        |> Changeset.change(%{name: "uq-after"})
+        |> TestRepo.upsert_and_log("concurrency-actor")
+
+      assert {:ok, %Resource{name: "uq-after"}} = result
+    end
   end
 
   describe "use inside Ecto.Multi (prevents nested multi tx RuntimeError)" do