diff --git a/projects/calendar_test.go b/projects/calendar_test.go
index f43e9b8..a5de167 100644
--- a/projects/calendar_test.go
+++ b/projects/calendar_test.go
@@ -15,6 +15,10 @@ func TestCalendarCreate(t *testing.T) {
 		t.Skip("Skipping test because the engine is not initialized")
 	}
 
+	// Only one blocked time calendar is allowed per user, so a leftover from an
+	// interrupted run makes the "all fields" case fail until it is removed.
+	deleteBlockedTimeCalendar(t)
+
 	tests := []struct {
 		name  string
 		input projects.CalendarCreateRequest
@@ -55,6 +59,35 @@ func TestCalendarCreate(t *testing.T) {
 	}
 }
 
+// deleteBlockedTimeCalendar removes the user's blocked time calendar if one
+// exists, so tests that create one start from a clean slate.
+func deleteBlockedTimeCalendar(t *testing.T) {
+	t.Helper()
+
+	ctx, cancel := context.WithTimeout(t.Context(), 10*time.Second)
+	t.Cleanup(cancel)
+
+	for request := projects.NewCalendarListRequest(); ; {
+		response, err := projects.CalendarList(ctx, engine, request)
+		if err != nil {
+			t.Fatalf("failed to list calendars: %s", err)
+		}
+		for _, calendar := range response.Calendars {
+			if calendar.Type != projects.CalendarTypeBlockedTime {
+				continue
+			}
+			if _, err := projects.CalendarDelete(ctx, engine, projects.NewCalendarDeleteRequest(calendar.ID)); err != nil {
+				t.Fatalf("failed to delete leftover blocked time calendar: %s", err)
+			}
+		}
+		next := response.Iterate()
+		if next == nil {
+			return
+		}
+		request = *next
+	}
+}
+
 func TestCalendarDelete(t *testing.T) {
 	if engine == nil {
 		t.Skip("Skipping test because the engine is not initialized")
diff --git a/projects/project.go b/projects/project.go
index a57fab5..beebeda 100644
--- a/projects/project.go
+++ b/projects/project.go
@@ -120,6 +120,10 @@ type Project struct {
 	// "deleted".
 	Status ProjectStatus `json:"status"`
 
+	// IsBillable indicates whether time logged to the project is billable by
+	// default.
+	IsBillable *bool `json:"isBillable"`
+
 	// Type is the type of the project. It can be "normal", "tasklists-template",
 	// "projects-template", "personal", "holder-project", "tentative" or
 	// "global-messages".
diff --git a/projects/sparse_fields_gen.go b/projects/sparse_fields_gen.go
index 175a74b..518b112 100644
--- a/projects/sparse_fields_gen.go
+++ b/projects/sparse_fields_gen.go
@@ -349,6 +349,7 @@ const (
 	ProjectFieldCompletedAt  ProjectField = "completedAt"
 	ProjectFieldCompletedBy  ProjectField = "completedBy"
 	ProjectFieldStatus       ProjectField = "status"
+	ProjectFieldIsBillable   ProjectField = "isBillable"
 	ProjectFieldType         ProjectField = "type"
 )