diff --git a/pioreactor/structs.py b/pioreactor/structs.py
index 13a7ec16..364aa251 100644
--- a/pioreactor/structs.py
+++ b/pioreactor/structs.py
@@ -210,7 +210,7 @@ def ipredict(self, y: Y, enforce_bounds=False) -> X:
 
         poly = self.curve_data_
 
-        coef_shift = zeros_like(poly)
+        coef_shift = zeros_like(poly, dtype=float)
         coef_shift[-1] = y
         solve_for_poly = poly - coef_shift
         roots_ = roots(solve_for_poly).tolist()
diff --git a/pioreactor/tests/test_calibrations.py b/pioreactor/tests/test_calibrations.py
index 4969f822..6488b32a 100644
--- a/pioreactor/tests/test_calibrations.py
+++ b/pioreactor/tests/test_calibrations.py
@@ -163,9 +163,9 @@ def test_ipredict_multiple_solutions(calibration) -> None:
 def test_ipredict_solution_below_domain(calibration) -> None:
     calibration.curve_data_ = [5, 3, 2]  # 5x^2 + 3x + 2
     calibration.recorded_data = {"x": [0, 1], "y": [10, 20]}
-    y = 100  # Solution below domain
+    y = 1.99  # Solution below domain
     with pytest.raises(exc.SolutionBelowDomainError):
-        calibration.ipredict(y)
+        calibration.ipredict(y, enforce_bounds=True)
 
 
 def test_ipredict_solution_above_domain(calibration) -> None:
@@ -173,7 +173,7 @@ def test_ipredict_solution_above_domain(calibration) -> None:
     calibration.recorded_data = {"x": [0, 1], "y": [0, 100]}
     y = 50  # Solution above domain
     with pytest.raises(exc.SolutionAboveDomainError):
-        calibration.ipredict(y)
+        calibration.ipredict(y, enforce_bounds=True)
 
 
 def test_predict_ipredict_consistency(calibration) -> None:
@@ -194,9 +194,9 @@ def test_linear_data_produces_linear_curve_in_range_even_if_high_degree() -> Non
     )
 
     od = np.insert(od, 0, 0)
-    v = 0.5 * od + 0.01 * np.random.randn(od.shape[0])
+    v = 0.5 * od + 0.005 * np.random.randn(od.shape[0])
 
-    curve_data_ = calculate_poly_curve_of_best_fit(v, od, degree=4)  # type: ignore
+    curve_data_ = calculate_poly_curve_of_best_fit(od, v, degree=4)  # type: ignore
     curve_callable = curve_to_callable("poly", curve_data_)
     for od_, v_ in zip(od, curve_callable(od)):
         assert (v_ - od_ * 0.5) < 0.035
diff --git a/pioreactor/tests/test_od_reading.py b/pioreactor/tests/test_od_reading.py
index 09bceb84..731ce3e0 100644
--- a/pioreactor/tests/test_od_reading.py
+++ b/pioreactor/tests/test_od_reading.py
@@ -1123,8 +1123,6 @@ def test_missing_calibration_data():
 
 
 def test_mandys_calibration():
-    from pioreactor.calibrations import load_calibration
-
     mcal = structs.ODCalibration(
         calibration_name="mandy",
         calibrated_on_pioreactor_unit="pio1",
@@ -1141,4 +1139,15 @@ def test_mandys_calibration():
         angle="90",
         pd_channel="2",
     )
+
+    with pytest.raises(exc.SolutionAboveDomainError):
+        assert 0.0 < mcal.ipredict(0.002, enforce_bounds=True) < 1.0
+
+    # correct the curve
+    mcal.curve_data_ = [
+        -0.028385470467897377,
+        0.12917002770232924,
+        0.07787877483987993,
+        0.0011023858538965646,
+    ]
     assert 0.0 < mcal.ipredict(0.002, enforce_bounds=True) < 1.0