diff --git a/rocketpy/utilities.py b/rocketpy/utilities.py
index 9ec707ffe..09083339d 100644
--- a/rocketpy/utilities.py
+++ b/rocketpy/utilities.py
@@ -283,7 +283,7 @@ def fin_flutter_analysis(
             flight,
         )
     if see_graphs:
-        _flutter_plots(flight, flutter_mach, safety_factor, filename)
+        _flutter_plots(flight, flutter_mach, safety_factor, filename=filename)
     else:
         return flutter_mach, safety_factor
 
diff --git a/tests/unit/test_utilities.py b/tests/unit/test_utilities.py
index 2bb8608b5..ce85f01de 100644
--- a/tests/unit/test_utilities.py
+++ b/tests/unit/test_utilities.py
@@ -117,6 +117,76 @@ def test_fin_flutter_analysis(flight_calisto_custom_wind):
     assert np.isclose(safety_factor(np.inf), 61.669562809629035, atol=5e-3)
 
 
+def test_fin_flutter_analysis_with_prints(flight_calisto_custom_wind):
+    """Test fin_flutter_analysis with see_prints=True to cover print branch.
+
+    Parameters
+    ----------
+    flight_calisto_custom_wind : Flight
+        A Flight object with a rocket with fins.
+    """
+    flutter_mach, safety_factor = utilities.fin_flutter_analysis(
+        fin_thickness=2 / 1000,
+        shear_modulus=10e9,
+        flight=flight_calisto_custom_wind,
+        see_prints=True,
+        see_graphs=False,  # False = returns tuple!
+        filename=None,
+    )
+
+    # Verify returns are valid
+    assert flutter_mach is not None
+    assert safety_factor is not None
+
+
+@patch("matplotlib.pyplot.show")
+def test_fin_flutter_analysis_with_graphs(mock_show, flight_calisto_custom_wind):  # pylint: disable=unused-argument
+    """Test fin_flutter_analysis with see_graphs=True to cover plotting branch.
+
+    Parameters
+    ----------
+    mock_show : mock
+        Mock of matplotlib.pyplot.show function.
+    flight_calisto_custom_wind : Flight
+        A Flight object with a rocket with fins.
+    """
+    result = utilities.fin_flutter_analysis(
+        fin_thickness=2 / 1000,
+        shear_modulus=10e9,
+        flight=flight_calisto_custom_wind,
+        see_prints=False,
+        see_graphs=True,  # True = returns None!
+        filename=None,
+    )
+
+    assert result is None
+    mock_show.assert_called()
+
+
+@patch("matplotlib.pyplot.show")
+def test_fin_flutter_analysis_complete_output(mock_show, flight_calisto_custom_wind):  # pylint: disable=unused-argument
+    """Test fin_flutter_analysis with both prints and graphs enabled.
+
+    Parameters
+    ----------
+    mock_show : mock
+        Mock of matplotlib.pyplot.show function.
+    flight_calisto_custom_wind : Flight
+        A Flight object with a rocket with fins.
+    """
+    result = utilities.fin_flutter_analysis(
+        fin_thickness=2 / 1000,
+        shear_modulus=10e9,
+        flight=flight_calisto_custom_wind,
+        see_prints=True,
+        see_graphs=True,  # True = returns None!
+        filename=None,
+    )
+
+    assert result is None
+    mock_show.assert_called()
+
+
 def test_flutter_prints(flight_calisto_custom_wind):
     """Tests the _flutter_prints function.