diff --git a/src/scgenerator/evaluator.py b/src/scgenerator/evaluator.py
index 95e9417..50c5086 100644
--- a/src/scgenerator/evaluator.py
+++ b/src/scgenerator/evaluator.py
@@ -465,7 +465,7 @@ default_rules: list[Rule] = [
     Rule("w_num", len, ["w"]),
     Rule("dw", lambda w: w[1] - w[0]),
     Rule(["fft", "ifft"], utils.fft_functions, priorities=1),
-    Rule("wavelength_window", lambda dt: (max(100e-9, 2 * units.c * dt), 8e-6)),
+    Rule("wavelength_window", lambda dt, wavelength: (math.min_wl_from_dt(dt, wavelength), 8e-6)),
     Rule("wavelength_window", fiber.valid_wavelength_window),
     Rule("dispersion_ind", fiber.dispersion_indices),
     # Pulse
diff --git a/src/scgenerator/math.py b/src/scgenerator/math.py
index 5a72267..fd24f90 100644
--- a/src/scgenerator/math.py
+++ b/src/scgenerator/math.py
@@ -271,7 +271,11 @@ def iwspace(w: np.ndarray, retstep: bool = False):
 
 
 def dt_from_min_wl(wl_min: float, wavelength: float) -> float:
-    return 0.5 * 1 / c * 1 / (1 / wl_min - 1 / wavelength)
+    return 0.5 / c / (1 / wl_min - 1 / wavelength)
+
+
+def min_wl_from_dt(dt: float, wavelength: float) -> float:
+    return wavelength / (1 + wavelength / (2 * c * dt))
 
 
 def _dt_from_wl_window(wavelength_window: tuple[float, float], wavelength: float) -> float:
diff --git a/tests/test_io_handlers.py b/tests/test_io_handlers.py
index 036b605..f8d648c 100644
--- a/tests/test_io_handlers.py
+++ b/tests/test_io_handlers.py
@@ -20,7 +20,6 @@ PARAMS = dict(
     # fiber
     dispersion_file="./PM2000D_2 extrapolated 4 0.npz",
     effective_area_file="./PM2000D_A_eff_marcuse.npz",
-    wavelength_window=(400e-9, 4000e-9),
     n2=4.5e-20,
     # simulation
     raman_type="measured",