diff --git a/internal/artifact/bk_uploader.go b/internal/artifact/bk_uploader.go
index 814eed5fb1..0142f61156 100644
--- a/internal/artifact/bk_uploader.go
+++ b/internal/artifact/bk_uploader.go
@@ -26,9 +26,8 @@ const artifactPathVariable = "${artifact:path}"
 
 const (
 	// BKUploader uploads to S3 either as:
-	// - a single signed POST, which has a hard limit of 5GB, or
-	// - as a signed multipart, which has a limit of 5GB per _part_, but we
-	//   aren't supporting larger artifacts yet.
+	// - a single signed POST, which has a hard limit of 5 GiB, or
+	// - as a signed multipart, which has a limit of 5 GiB per part.
 	// Note that multipart parts have a minimum size of 5MB.
 	maxFormUploadedArtifactSize = int64(5 * 1024 * 1024 * 1024)
 )
@@ -61,9 +60,10 @@ func NewBKUploader(l logger.Logger, c BKUploaderConfig) *BKUploader {
 // it is provided by Buildkite after uploading.
 func (u *BKUploader) URL(*api.Artifact) string { return "" }
 
-// CreateWork checks the artifact size, then creates one worker.
+// CreateWork creates workers for the artifact's upload instructions.
 func (u *BKUploader) CreateWork(artifact *api.Artifact) ([]workUnit, error) {
-	if artifact.FileSize > maxFormUploadedArtifactSize {
+	if artifact.FileSize > maxFormUploadedArtifactSize &&
+		(artifact.UploadInstructions == nil || len(artifact.UploadInstructions.Actions) == 0) {
 		return nil, errArtifactTooLarge{Size: artifact.FileSize}
 	}
 	actions := artifact.UploadInstructions.Actions
@@ -383,5 +383,5 @@ type errArtifactTooLarge struct {
 func (e errArtifactTooLarge) Error() string {
 	// TODO: Clean up error strings
 	// https://github.com/golang/go/wiki/CodeReviewComments#error-strings
-	return fmt.Sprintf("File size (%d bytes) exceeds the maximum supported by Buildkite's default artifact storage (5Gb). Alternative artifact storage options may support larger files.", e.Size)
+	return fmt.Sprintf("File size (%d bytes) exceeds the 5 GiB limit for a single upload to Buildkite artifact storage. Multipart upload instructions are required for larger files.", e.Size)
 }
diff --git a/internal/artifact/bk_uploader_test.go b/internal/artifact/bk_uploader_test.go
index 0a4fd6bd1f..15888b45ff 100644
--- a/internal/artifact/bk_uploader_test.go
+++ b/internal/artifact/bk_uploader_test.go
@@ -293,19 +293,62 @@ func TestFormUploadFileMissing(t *testing.T) {
 
 func TestFormUploadTooBig(t *testing.T) {
 	uploader := NewBKUploader(logger.Discard, BKUploaderConfig{})
-	const size = int64(6442450944) // 6Gb
+	const size = int64(6 * 1024 * 1024 * 1024) // 6 GiB
+	for _, test := range []struct {
+		name         string
+		instructions *api.ArtifactUploadInstructions
+	}{
+		{name: "no actions", instructions: &api.ArtifactUploadInstructions{}},
+		{name: "nil instructions"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			artifact := &api.Artifact{
+				ID:                 "xxxxx-xxxx-xxxx-xxxx-xxxxxxxxxx",
+				Path:               "llamas.txt",
+				AbsolutePath:       "/llamas.txt",
+				GlobPath:           "llamas.txt",
+				ContentType:        "text/plain",
+				FileSize:           size,
+				UploadInstructions: test.instructions,
+			}
+
+			wantErr := errArtifactTooLarge{Size: size}
+			if _, err := uploader.CreateWork(artifact); !errors.Is(err, wantErr) {
+				t.Fatalf("uploader.CreateWork(artifact) error = %v, want %v", err, wantErr)
+			}
+		})
+	}
+}
+
+func TestMultipartUploadAboveFormLimit(t *testing.T) {
+	uploader := NewBKUploader(logger.Discard, BKUploaderConfig{})
+	const size = int64(5*1024*1024*1024 + 1)
+	actions := []api.ArtifactUploadAction{
+		{URL: "https://example.com/part-2", Method: "PUT", PartNumber: 2},
+		{URL: "https://example.com/part-1", Method: "PUT", PartNumber: 1},
+	}
 	artifact := &api.Artifact{
-		ID:                 "xxxxx-xxxx-xxxx-xxxx-xxxxxxxxxx",
-		Path:               "llamas.txt",
-		AbsolutePath:       "/llamas.txt",
-		GlobPath:           "llamas.txt",
-		ContentType:        "text/plain",
-		FileSize:           size,
-		UploadInstructions: &api.ArtifactUploadInstructions{},
+		ID:       "xxxxx-xxxx-xxxx-xxxx-xxxxxxxxxx",
+		Path:     "llamas.txt",
+		FileSize: size,
+		UploadInstructions: &api.ArtifactUploadInstructions{
+			Actions: actions,
+		},
 	}
 
-	wantErr := errArtifactTooLarge{Size: size}
-	if _, err := uploader.CreateWork(artifact); !errors.Is(err, wantErr) {
-		t.Fatalf("uploader.CreateWork(artifact) error = %v, want %v", err, wantErr)
+	work, err := uploader.CreateWork(artifact)
+	if err != nil {
+		t.Fatalf("uploader.CreateWork(artifact) error = %v", err)
+	}
+
+	want := []workUnit{
+		&bkMultipartUpload{BKUploader: uploader, artifact: artifact, partCount: 2, action: &actions[0], offset: 0, size: size/2 + 1},
+		&bkMultipartUpload{BKUploader: uploader, artifact: artifact, partCount: 2, action: &actions[1], offset: size/2 + 1, size: size / 2},
+	}
+	if diff := cmp.Diff(work, want,
+		cmp.AllowUnexported(bkMultipartUpload{}),
+		cmpopts.EquateComparable(uploader),
+	); diff != "" {
+		t.Fatalf("CreateWork diff (-got +want):\n%s", diff)
 	}
 }