diff --git a/src/nmreval/models/wideline.py b/src/nmreval/models/wideline.py
index 79ec918..301463a 100644
--- a/src/nmreval/models/wideline.py
+++ b/src/nmreval/models/wideline.py
@@ -176,8 +176,8 @@ class CzjzekCT:
     type = 'Spectrum'
     name = 'Czjzek (Central Line)'
     equation = ''
-    params = ['A', r'\sigma', 'GB', r'\omega_{L}']
-    bounds = [(0, None), (0, None), (0, None), (0, None)]
+    params = ['A', r'\sigma', r'f_{iso}', 'GB', r'\omega_{L}']
+    bounds = [(0, None), (0, None), (None, None), (0, None), (0, None)]
     choices = [('Spin', 'spin', {'3/2': 1.5, '5/2': 2.5}),
                ('Broadening', 'broad', {'Gaussian': 'g', 'Lorentzian': 'l'})]
 
@@ -186,6 +186,7 @@ class CzjzekCT:
             x: np.ndarray,
             c: float,
             sigma: float,
+            f_iso: float,
             gb: float,
             f_l: float,
             spin: float = 1.5,
@@ -218,7 +219,7 @@ class CzjzekCT:
         orient += prefactor_b * cos_theta_square
         orient += prefactor_c
 
-        vQ = -orient[..., None] * coupling[None, None, :]
+        vQ = -(orient[..., None] * coupling[None, None, :]) + f_iso
         weights = np.ones_like(vQ) * dist
 
         bins = _make_bins(x)
@@ -239,4 +240,5 @@ class CzjzekCT:
 
     @staticmethod
     def czjzek(cq, eta, sigma):
-        return np.exp(-cq ** 2 * (1 + eta**2 / 3) / 2 / sigma**2) * cq**4 * eta * (1 - eta**2 / 9) * np.sqrt(2 / np.pi) / sigma**5
+        return np.exp(-cq ** 2 * (1 + eta ** 2 / 3) / 2 / sigma ** 2) * cq ** 4 * eta * (
+                    1 - eta ** 2 / 9) * np.sqrt(2 / np.pi) / sigma ** 5