diff --git a/frontend/src/app/shared/components/datepicker/multi-date-modal/multi-date.modal.ts b/frontend/src/app/shared/components/datepicker/multi-date-modal/multi-date.modal.ts
index 3da29a5d8c..99d8b2fa23 100644
--- a/frontend/src/app/shared/components/datepicker/multi-date-modal/multi-date.modal.ts
+++ b/frontend/src/app/shared/components/datepicker/multi-date-modal/multi-date.modal.ts
@@ -213,7 +213,8 @@ export class MultiDateModalComponent extends OpModalComponent implements AfterVi
     .pipe(
       this.untilDestroyed(),
       debounceTime(500),
-      map((value) => (value === '' ? null : parseInt(value, 10))),
+      map((value) => (value === '' ? null : Math.abs(parseInt(value, 10)))),
+      filter((val) => val === null || !Number.isNaN(val)),
       filter((val) => val !== this.duration),
     )
     .subscribe((value) => this.applyDurationChange(value));
diff --git a/spec/features/work_packages/details/date_editor_spec.rb b/spec/features/work_packages/details/date_editor_spec.rb
index 05cd0f1e43..ed146bb5a3 100644
--- a/spec/features/work_packages/details/date_editor_spec.rb
+++ b/spec/features/work_packages/details/date_editor_spec.rb
@@ -233,6 +233,17 @@ describe 'date inplace editor',
     start_date.expect_state_text "#{Time.zone.today.strftime('%Y-%m-%d')} - #{Time.zone.today.strftime('%Y-%m-%d')}"
   end
 
+  it 'can set a negative duration which gets transformed (Regression #44219)' do
+    start_date.activate!
+    start_date.expect_active!
+
+    start_date.datepicker.expect_visible
+    start_date.datepicker.set_duration -128
+    start_date.datepicker.focus_start_date
+
+    start_date.datepicker.expect_duration 128
+  end
+
   it 'saves the date when clearing and then confirming' do
     start_date.activate!