diff --git a/backend/bills/internal/adapter/sqlite/repository.go b/backend/bills/internal/adapter/sqlite/repository.go
index 3fc593d6..b39b5e20 100644
--- a/backend/bills/internal/adapter/sqlite/repository.go
+++ b/backend/bills/internal/adapter/sqlite/repository.go
@@ -174,6 +174,10 @@ func (r *Repository) GetBillVersionDiff(ctx context.Context, id, fromVersionID,
 	if err != nil {
 		return nil, err
 	}
+
+	if ok, err := r.tableExists(ctx, "bill_versions"); err != nil || !ok {
+		return nil, err
+	}
 	if ok, err := r.tableExists(ctx, "bill_diffs"); err != nil || !ok {
 		return nil, err
 	}
@@ -181,6 +185,22 @@ func (r *Repository) GetBillVersionDiff(ctx context.Context, id, fromVersionID,
 		return nil, err
 	}
 
+	fromVersion, ok, err := r.billVersionByID(ctx, billID, fromVersionID)
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		return nil, usecase.ErrVersionNotFound
+	}
+
+	toVersion, ok, err := r.billVersionByID(ctx, billID, toVersionID)
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		return nil, usecase.ErrVersionNotFound
+	}
+
 	var diffID string
 	err = r.db.QueryRowContext(ctx, `
 		SELECT id
@@ -194,14 +214,6 @@ func (r *Repository) GetBillVersionDiff(ctx context.Context, id, fromVersionID,
 		return nil, fmt.Errorf("query bill diff sqlite artifact: %w", err)
 	}
 
-	fromVersion, ok, err := r.billVersionByID(ctx, billID, fromVersionID)
-	if err != nil || !ok {
-		return nil, err
-	}
-	toVersion, ok, err := r.billVersionByID(ctx, billID, toVersionID)
-	if err != nil || !ok {
-		return nil, err
-	}
 	clauses, err := r.billClauseDiffs(ctx, billID, diffID)
 	if err != nil {
 		return nil, err
diff --git a/backend/bills/internal/adapter/sqlite/repository_test.go b/backend/bills/internal/adapter/sqlite/repository_test.go
index 24875eb6..bf4fbd2c 100644
--- a/backend/bills/internal/adapter/sqlite/repository_test.go
+++ b/backend/bills/internal/adapter/sqlite/repository_test.go
@@ -46,12 +46,26 @@ func TestRepositoryGetBillVersionDiffMapsCurrentArtifactSchema(t *testing.T) {
 	}
 }
 
-func TestRepositoryGetBillVersionDiffReturnsNilForUnknownVersionPair(t *testing.T) {
+func TestRepositoryGetBillVersionDiffReturnsVersionNotFoundForUnknownVersionPair(t *testing.T) {
 	db := openDiffFixtureDB(t)
 	defer db.Close()
 	repo := New(db)
 
 	diff, err := repo.GetBillVersionDiff(context.Background(), "C-2", "v1", "missing")
+	if !errors.Is(err, usecase.ErrVersionNotFound) {
+		t.Fatalf("error = %v, want ErrVersionNotFound", err)
+	}
+	if diff != nil {
+		t.Fatalf("diff = %+v, want nil", diff)
+	}
+}
+
+func TestRepositoryGetBillVersionDiffReturnsNilWhenVersionsExistButNoDiff(t *testing.T) {
+	db := openDiffFixtureDB(t)
+	defer db.Close()
+	repo := New(db)
+
+	diff, err := repo.GetBillVersionDiff(context.Background(), "C-2", "v2", "v1")
 	if err != nil {
 		t.Fatalf("GetBillVersionDiff error: %v", err)
 	}
diff --git a/backend/bills/internal/usecase/open_bills_index.go b/backend/bills/internal/usecase/open_bills_index.go
index a605a808..5c90da3a 100644
--- a/backend/bills/internal/usecase/open_bills_index.go
+++ b/backend/bills/internal/usecase/open_bills_index.go
@@ -14,6 +14,7 @@ var (
 	ErrBillNotFound     = errors.New("bill not found")
 	ErrDiffMissingFrom  = errors.New("missing required from version id")
 	ErrDiffMissingTo    = errors.New("missing required to version id")
+	ErrVersionNotFound  = errors.New("version not found")
 )
 
 type ManifestLoader interface {
diff --git a/backend/bills/main.go b/backend/bills/main.go
index 03170bd6..e9a0f3b8 100644
--- a/backend/bills/main.go
+++ b/backend/bills/main.go
@@ -288,6 +288,8 @@ func mapBillVersionDiffError(err error) events.APIGatewayProxyResponse {
 		return jsonError(http.StatusBadRequest, "missing required query parameter: to")
 	case errors.Is(err, usecase.ErrBillNotFound):
 		return jsonError(http.StatusNotFound, "bill not found")
+	case errors.Is(err, usecase.ErrVersionNotFound):
+		return jsonError(http.StatusNotFound, "version not found")
 	default:
 		slog.Error("load bill version diff request failed", "error", err)
 		return jsonError(http.StatusInternalServerError, "internal error")
diff --git a/backend/bills/main_test.go b/backend/bills/main_test.go
index 4efa0c65..d3221179 100644
--- a/backend/bills/main_test.go
+++ b/backend/bills/main_test.go
@@ -215,7 +215,7 @@ func TestHandleRequestBillVersionDiffUnknownBillReturns404(t *testing.T) {
 	}
 }
 
-func TestHandleRequestBillVersionDiffUnknownVersionsReturnsNoContent(t *testing.T) {
+func TestHandleRequestBillVersionDiffUnknownVersionsReturns404(t *testing.T) {
 	dir := t.TempDir()
 	p45 := 45
 	writeBillSQLiteUnitFixture(t, dir, []Bill{
@@ -230,12 +230,12 @@ func TestHandleRequestBillVersionDiffUnknownVersionsReturnsNoContent(t *testing.
 	if err != nil {
 		t.Fatalf("HandleRequest error: %v", err)
 	}
-	if resp.StatusCode != 204 {
+	if resp.StatusCode != 404 {
 		t.Fatalf("status = %d, body = %s", resp.StatusCode, resp.Body)
 	}
 }
 
-func TestHandleRequestBillVersionDiffOneVersionBillReturnsNoContent(t *testing.T) {
+func TestHandleRequestBillVersionDiffOneVersionBillReturns404(t *testing.T) {
 	dir := t.TempDir()
 	p45 := 45
 	writeBillSQLiteUnitFixture(t, dir, []Bill{
@@ -250,6 +250,26 @@ func TestHandleRequestBillVersionDiffOneVersionBillReturnsNoContent(t *testing.T
 	if err != nil {
 		t.Fatalf("HandleRequest error: %v", err)
 	}
+	if resp.StatusCode != 404 {
+		t.Fatalf("status = %d, body = %s", resp.StatusCode, resp.Body)
+	}
+}
+
+func TestHandleRequestBillVersionDiffVersionsExistButNoDiffReturns204(t *testing.T) {
+	dir := t.TempDir()
+	p45 := 45
+	writeBillSQLiteUnitFixture(t, dir, []Bill{
+		{ID: "C-2287", Number: "C-2287", Title: "Diff Act", Status: "InProgress", Parliament: &p45},
+	})
+	withLocalIndex(t, dir)
+
+	resp, err := HandleRequest(context.Background(), events.APIGatewayProxyRequest{
+		Path:                  "/api/v1/bills/C-2287/diff",
+		QueryStringParameters: map[string]string{"from": "C-2287-v2", "to": "C-2287-v1"},
+	})
+	if err != nil {
+		t.Fatalf("HandleRequest error: %v", err)
+	}
 	if resp.StatusCode != 204 {
 		t.Fatalf("status = %d, body = %s", resp.StatusCode, resp.Body)
 	}