Inclusion Criteria:  Signed and dated informed consent obtained before any trial-related activities. Trial-related activities are any procedures that would not have been done during normal management of the subject. Subjects with type 1 diabetes mellitus. Body Mass Index (BMI) between 25.0 and 35.0 kg/m^2, both inclusive. HbA1c between 7.0 % and 9.5 %, both inclusive. Diabetes duration of at least 12 months. Using a multiple dosing insulin therapy (MDI) with a basal insulin and a rapid-acting insulin at at least two meals per day. Using any CGM or Flash Glucose Monitoring (FGM) for at least 1 month or willing to use CGM during the trial.  Exclusion Criteria:  Known or suspected hypersensitivity to IMPs or any of the excipients or to any component of the IMP formulation. Type 2 diabetes mellitus. Receipt of any medicinal product in clinical development within 3 months or at least 5 half-lives of the related substances and their metabolites (whichever is longer) before randomisation in this trial. History of multiple and/or severe allergies to drugs or foods or a history of severe anaphylactic reaction. Any history or presence of cancer except basal cell skin cancer or squamous cell skin cancer as judged by the Investigator. Clinically significant abnormal screening laboratory tests, as judged by the Investigator. Systolic blood pressure < 90 mmHg or >139 mmHg and/or diastolic blood pressure < 50 mmHg or > 89 mmHg. One repeat test (on a different day, if necessary) will be acceptable in case of suspected white-coat hypertension. Clinically significant abnormal standard 12-lead electrocardiogram (ECG) after 5 minutes resting in supine position at screening, as judged by the Investigator. Proliferative retinopathy or maculopathy as judged by the Investigator based on a recent (<1.5 years) ophthalmologic examination. Severe neuropathy, in particular autonomic neuropathy, as judged by the Investigator. More than one episode of severe hypoglycaemia with seizure, coma or requiring assistance of another person during the past 6 months. Hypoglycaemic unawareness as judged by the Investigator. Hospitalisation for diabetic ketoacidosis during the previous 6 months. Presence of clinically significant gastrointestinal symptoms (e.g., nausea, vomiting, heartburn or diarrhea), as judged by the Investigator. Confirmed diagnosis of gastroparesis or requiring the use of drugs that alter gastrointestinal motility. Unusual meal habits and special diet requirements that could constitute a risk for the subject when participating in the trial or interfere with the interpretation of data. Use of oral antidiabetic drugs (OADs) and/or GLP-1 receptor agonists within 4 weeks prior to screening. Use of systemic glucocorticoid therapy (excluding topical, intraocular, intranasal, intra-articular, or inhaled preparations) within 2 months prior to screening. Use or planned use of drugs that promote weight loss (e.g. liraglutide, semaglutide, orlistat, lorcaserin, phentermine) within 2 months prior to screening. If female, pregnancy or breast-feeding. Women of childbearing potential who are not using a highly effective contraceptive method. The Investigator considers a subject as unsuitable for inclusion in the study for any other reason.