diff --git a/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs b/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs
index edc4498..db7130f 100644
--- a/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs
+++ b/LehrerApp.Desktop.Tests/TimetableViewModelTests.cs
@@ -262,6 +262,27 @@ public sealed class TimetableViewModelTests
         Assert.False(cell.HasExperiment);
     }
 
+    [Fact]
+    public void Load_Wochenkachel_UnvollstaendigePhasendaten_VerursachenKeinenFehler()
+    {
+        var group = new LearningGroup { Name = "Q1 Chemie" };
+        var date = DateInCurrentWeek(DayOfWeek.Monday);
+        var slots = new FakeTimetableSlots();
+        slots.Add(new TimetableSlot { GroupId = group.Id, Weekday = DayOfWeek.Monday, PeriodNumber = 1 });
+        var lessons = new FakeLessons();
+        lessons.Add(new Lesson
+        {
+            GroupId = group.Id,
+            Date = date,
+            Phases = [new LessonPhaseStep { Name = null!, Activity = null!, Material = "Experimentiermaterial" }],
+        });
+
+        var vm = BuildViewModel(slots, new FakeGroups([group]), lessons: lessons);
+
+        var cell = vm.WeekItems.Single(c => c.IsSlotCell && c.Weekday == DayOfWeek.Monday && c.PeriodNumber == 1);
+        Assert.True(cell.HasExperiment);
+    }
+
     [Fact]
     public void Load_Wochenkachel_LetzteStundeVorKlausur_ZeigtIcon()
     {
diff --git a/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs b/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs
index d4452a9..a93da1f 100644
--- a/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs
+++ b/LehrerApp.Desktop/ViewModels/Planning/TimetableViewModel.cs
@@ -387,10 +387,10 @@ public partial class TimetableViewModel : ObservableObject
     }
 
     private static bool MentionsExperiment(Lesson? lesson) =>
-        lesson is not null && lesson.Phases.Any(p =>
-            p.Name.Contains("Experiment", StringComparison.OrdinalIgnoreCase) ||
-            p.Activity.Contains("Experiment", StringComparison.OrdinalIgnoreCase) ||
-            p.Material.Contains("Experiment", StringComparison.OrdinalIgnoreCase));
+        lesson?.Phases?.Any(p => p is not null &&
+            (p.Name?.Contains("Experiment", StringComparison.OrdinalIgnoreCase) == true ||
+             p.Activity?.Contains("Experiment", StringComparison.OrdinalIgnoreCase) == true ||
+             p.Material?.Contains("Experiment", StringComparison.OrdinalIgnoreCase) == true)) == true;
 
     /// <summary>Fällt <paramref name="date"/> auf einen gesetzlichen Feiertag oder in Schulferien?</summary>
     private static bool IsFreeDay(DateOnly date, List<SchoolHoliday> schoolHolidays, HashSet<DateOnly> publicHolidayDates) =>