diff --git a/CHANGELOG.md b/CHANGELOG.md
index 05277e667..9649508b4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed `AddWorkerSafely` leaving a worker's primary kind and earlier aliases registered when a later kind alias conflicts with an existing registration. Failed registrations now leave the worker registry unchanged. [PR #1440](https://github.com/riverqueue/river/pull/1440).
+
 ## [0.49.0] - 2026-10-05
 
 ### Changed
diff --git a/worker.go b/worker.go
index f833b760d..0c1ede252 100644
--- a/worker.go
+++ b/worker.go
@@ -162,32 +162,26 @@ func NewWorkers() *Workers {
 }
 
 func (w Workers) add(jobArgs JobArgs, workUnitFactory workunit.WorkUnitFactory) error {
-	checkRegistered := func(kind string) error {
-		if _, ok := w.workersMap[kind]; ok {
+	kinds := []string{jobArgs.Kind()}
+	if args, ok := jobArgs.(JobArgsWithKindAliases); ok {
+		kinds = append(kinds, args.KindAliases()...)
+	}
+
+	// Validate all kinds before changing the registry.
+	seen := make(map[string]bool, len(kinds))
+	for _, kind := range kinds {
+		if _, ok := w.workersMap[kind]; ok || seen[kind] {
 			return fmt.Errorf("worker for kind %q is already registered", kind)
 		}
-		return nil
+		seen[kind] = true
 	}
 
-	workerInfo := workerInfo{
+	info := workerInfo{
 		jobArgs:         jobArgs,
 		workUnitFactory: workUnitFactory,
 	}
-
-	kind := jobArgs.Kind()
-	if err := checkRegistered(kind); err != nil {
-		return err
-	}
-	w.workersMap[kind] = workerInfo
-
-	// Jobs can register an alternate kind to make renaming easier.
-	if jobArgsWithKindAliases, ok := jobArgs.(JobArgsWithKindAliases); ok {
-		for _, kind := range jobArgsWithKindAliases.KindAliases() {
-			if err := checkRegistered(kind); err != nil {
-				return err
-			}
-			w.workersMap[kind] = workerInfo
-		}
+	for _, kind := range kinds {
+		w.workersMap[kind] = info
 	}
 
 	return nil
diff --git a/worker_test.go b/worker_test.go
index 8654b21ba..5fa58121e 100644
--- a/worker_test.go
+++ b/worker_test.go
@@ -13,6 +13,19 @@ import (
 	"github.com/riverqueue/river/rivershared/util/testutil"
 )
 
+func TestAddWorkerSafelyAliasCollisionDoesNotRegisterKinds(t *testing.T) {
+	t.Parallel()
+
+	workers := NewWorkers()
+
+	require.NoError(t, AddWorkerSafely(workers, WorkFunc(func(context.Context, *Job[withKindAliasesArgs]) error { return nil })))
+	before := len(workers.workersMap)
+	require.Error(t, AddWorkerSafely(workers, WorkFunc(func(context.Context, *Job[lateAliasCollisionArgs]) error { return nil })))
+	require.Len(t, workers.workersMap, before)
+	require.NotContains(t, workers.workersMap, "candidate_primary")
+	require.NotContains(t, workers.workersMap, "candidate_early_alias")
+}
+
 func TestWork(t *testing.T) {
 	t.Parallel()
 
@@ -74,6 +87,13 @@ func (w *configurableWorker) Work(ctx context.Context, job *Job[configurableArgs
 	return nil
 }
 
+type lateAliasCollisionArgs struct{}
+
+func (lateAliasCollisionArgs) Kind() string { return "candidate_primary" }
+func (lateAliasCollisionArgs) KindAliases() []string {
+	return []string{"candidate_early_alias", "with_kind_alternate_alternate"}
+}
+
 type withKindAliasesArgs struct{}
 
 func (a withKindAliasesArgs) Kind() string          { return "with_kind_alternate" }