diff --git a/esbo_etc/classes/sensor/Heterodyne.py b/esbo_etc/classes/sensor/Heterodyne.py
index 3c1187e..1259a5c 100644
--- a/esbo_etc/classes/sensor/Heterodyne.py
+++ b/esbo_etc/classes/sensor/Heterodyne.py
@@ -121,7 +121,7 @@ class Heterodyne(ASensor):
         # Calculate the signal and background temperatures
         t_signal, t_background = self.calcTemperatures(background, signal, obstruction)
         line_ind = np.where(t_signal.wl == self.__lambda_line)[0][0]
-        t_sys = 2 * (t_background + self.__receiver_temp)
+        t_sys = 2 * (t_background + self.__receiver_temp + t_signal)
         # Calculate the noise bandwidth
         delta_nu = t_signal.wl.to(u.Hz, equivalencies=u.spectral()) / (t_signal.wl / self.__common_conf.wl_delta() + 1)
         exp_time = []
@@ -172,7 +172,7 @@ class Heterodyne(ASensor):
         # Calculate the signal and background temperatures
         t_signal, t_background = self.calcTemperatures(background, signal, obstruction)
         line_ind = np.where(t_signal.wl == self.__lambda_line)[0][0]
-        t_sys = 2 * (t_background + self.__receiver_temp)
+        t_sys = 2 * (t_background + self.__receiver_temp + t_signal)
         # Calculate the noise bandwidth
         delta_nu = t_signal.wl.to(u.Hz, equivalencies=u.spectral()) / (t_signal.wl / self.__common_conf.wl_delta() + 1)
         sensitivity = []
diff --git a/tests/sensor/test_Heterodyne.py b/tests/sensor/test_Heterodyne.py
index a42c30d..e6b75fb 100644
--- a/tests/sensor/test_Heterodyne.py
+++ b/tests/sensor/test_Heterodyne.py
@@ -25,7 +25,7 @@ class TestHeterodyne(TestCase):
 
     def test_getSNR(self):
         snr = self.heterodyne.getSNR(1900 * u.s)
-        self.assertAlmostEqual(snr.value, 10.059625717085497)
+        self.assertAlmostEqual(snr.value, 10.17992964320754)
 
     def test_getExpTime(self):
         exp_time = 1900 * u.s