diff --git a/advlabdb/models.py b/advlabdb/models.py
index be3a2e4..1697f9a 100644
--- a/advlabdb/models.py
+++ b/advlabdb/models.py
@@ -535,11 +535,12 @@ class ExperimentMark(db.Model):
         return ExperimentMark(part_student=part_student, group_experiment=group_experiment)
 
     def updateFinalExperimentMark(self):
-        semesterExperiment = self.group_experiment.semester_experiment
-        self.final_experiment_mark = roundHalfUpToInt(
-            semesterExperiment.oral_weighting * self.oral_mark
-            + semesterExperiment.protocol_weighting * self.protocol_mark
-        )
+        if None not in (self.oral_mark, self.protocol_mark):
+            semesterExperiment = self.group_experiment.semester_experiment
+            self.final_experiment_mark = roundHalfUpToInt(
+                semesterExperiment.oral_weighting * self.oral_mark
+                + semesterExperiment.protocol_weighting * self.protocol_mark
+            )
 
     def repr(self):
         return f"Mark {self.final_experiment_mark}; Exp {self.group_experiment.semester_experiment.repr()}"