diff --git a/src/model_modules/linear_model.py b/src/model_modules/linear_model.py
index 3d5323e1b0303b497c1f26c4e84ee9b968380425..933a108c1b06e1786f75e7f4ebd9b220fbe812dd 100644
--- a/src/model_modules/linear_model.py
+++ b/src/model_modules/linear_model.py
@@ -31,7 +31,7 @@ class OrdinaryLeastSquaredModel:
         self.y = data_y
 
     def predict(self, data):
-        data = sm.add_constant(self.reshape_xarray_to_numpy(data))
+        data = sm.add_constant(self.reshape_xarray_to_numpy(data), has_constant="add")
         return np.atleast_2d(self.model.predict(data))
 
     @staticmethod
diff --git a/test/test_model_modules/test_linear_model.py b/test/test_model_modules/test_linear_model.py
new file mode 100644
index 0000000000000000000000000000000000000000..e4e10e9db04ba041d61d6ebcf5de3a23380c8ebe
--- /dev/null
+++ b/test/test_model_modules/test_linear_model.py
@@ -0,0 +1,8 @@
+
+from src.model_modules.linear_model import OrdinaryLeastSquaredModel
+
+
+class TestOrdinaryLeastSquareModel:
+
+    def test_constant_input_variable(self):
+        pass