diff --git a/libra_toolbox/tritium/lsc_measurements.py b/libra_toolbox/tritium/lsc_measurements.py
index 77b81ee..6fd916c 100644
--- a/libra_toolbox/tritium/lsc_measurements.py
+++ b/libra_toolbox/tritium/lsc_measurements.py
@@ -73,6 +73,11 @@ def substract_background(self, background_sample: "LSCSample"):
         if self.background_substracted:
             raise ValueError("Background already substracted")
         self.activity -= background_sample.activity
+        if self.activity.magnitude < 0:
+            warnings.warn(
+                f"Activity of {self.name} is negative after substracting background. Setting to zero."
+            )
+            self.activity = 0 * ureg.Bq
         self.background_substracted = True
 
     @staticmethod
diff --git a/test/tritium/test_lsc_samples.py b/test/tritium/test_lsc_samples.py
index 1c550ca..ab18423 100644
--- a/test/tritium/test_lsc_samples.py
+++ b/test/tritium/test_lsc_samples.py
@@ -35,6 +35,18 @@ def test_lscsample_substract_background():
         sample.substract_background(background_sample)
 
 
+def test_lscsample_substract_background_when_negative():
+    sample = LSCSample(0.5 * ureg.Bq, "Sample1")
+    background_sample = LSCSample(1.0 * ureg.Bq, "Background")
+    with pytest.warns(
+        UserWarning,
+        match=f"Activity of {sample.name} is negative after substracting background. Setting to zero.",
+    ):
+        sample.substract_background(background_sample)
+    assert sample.activity == 0 * ureg.Bq
+    assert sample.background_substracted
+
+
 def test_lscsample_from_file():
     file_reader = LSCFileReader(
         Path(__file__).parent / "TEST_CSV.csv",