diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3bdbb9a..16a4878 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
+
+- Declare `unique_constraint` on the audit_log pkey inside `changelog_changeset/1` so `update_and_log` (and other `*_and_log` / `log` paths) do not raise `Ecto.ConstraintError` on `audit_logs_pkey` when the log table's sequence produces a colliding id. Closes OPS-4594.
+
 ## [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..0ebec78 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_table Application.compile_env(:ecto_trail, :table_name, "audit_log")
+  @pkey_constraint_name "#{@audit_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: @pkey_constraint_name)
   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..d59f42c 100644
--- a/test/unit/ecto_trail_test.exs
+++ b/test/unit/ecto_trail_test.exs
@@ -329,4 +329,34 @@ defmodule EctoTrailTest do
                )
     end
   end
+
+  describe "update_and_log/3 pkey constraint resilience" do
+    setup do
+      {:ok, schema} = TestRepo.insert(%Resource{name: "name"})
+      {:ok, %{schema: schema}}
+    end
+
+    test "does not raise Ecto.ConstraintError on audit_log pkey collision; main update succeeds and log failure is swallowed",
+         %{schema: schema} do
+      # Force a deterministic pkey collision for the *next* library-generated insert.
+      # Insert a colliding row with an explicit id, then setval so the sequence will emit the same id.
+      TestRepo.query!("""
+        INSERT INTO audit_log (id, actor_id, resource, resource_id, changeset, change_type, inserted_at)
+        VALUES (987654, 'seed', 'resources', '1', '{}', 'update', now())
+      """)
+
+      TestRepo.query!("SELECT setval('audit_log_id_seq', 987653, true)")
+
+      # The upcoming log insert inside update_and_log will use nextval()=987654 and hit pkey dup.
+      # Before the fix: raises Ecto.ConstraintError (see OPS-4594 stack).
+      # After the fix: unique_constraint turns it into a changeset error; log_changes swallows it (logs + {:ok, reason}).
+      result =
+        schema
+        |> Changeset.change(%{name: "name-after-collision"})
+        |> TestRepo.update_and_log("constraint-actor")
+
+      assert {:ok, %Resource{name: "name-after-collision"}} = result
+      assert [%{name: "name-after-collision"}] = TestRepo.all(Resource)
+    end
+  end
 end