diff --git a/bilby/gw/prior.py b/bilby/gw/prior.py
index 54f803401cac2f64eeaaca46d307eba68d7efc7d..1f605f56f1a85509b09f0fc55e75e491aa7f3a63 100644
--- a/bilby/gw/prior.py
+++ b/bilby/gw/prior.py
@@ -1183,7 +1183,7 @@ class CalibrationPriorDict(PriorDict):
     @staticmethod
     def constant_uncertainty_spline(
             amplitude_sigma, phase_sigma, minimum_frequency, maximum_frequency,
-            n_nodes, label):
+            n_nodes, label, boundary="reflective"):
         """
         Make prior assuming constant in frequency calibration uncertainty.
 
@@ -1203,6 +1203,8 @@ class CalibrationPriorDict(PriorDict):
             Number of nodes for the spline.
         label: str
             Label for the names of the parameters, e.g., `recalib_H1_`
+        boundary: None, 'reflective', 'periodic'
+            The type of prior boundary to assign
 
         Returns
         =======
@@ -1225,14 +1227,14 @@ class CalibrationPriorDict(PriorDict):
             prior[name] = Gaussian(mu=amplitude_mean_nodes[ii],
                                    sigma=amplitude_sigma_nodes[ii],
                                    name=name, latex_label=latex_label,
-                                   boundary='reflective')
+                                   boundary=boundary)
         for ii in range(n_nodes):
             name = "recalib_{}_phase_{}".format(label, ii)
             latex_label = r"$\phi^{}_{}$".format(label, ii)
             prior[name] = Gaussian(mu=phase_mean_nodes[ii],
                                    sigma=phase_sigma_nodes[ii],
                                    name=name, latex_label=latex_label,
-                                   boundary='reflective')
+                                   boundary=boundary)
         for ii in range(n_nodes):
             name = "recalib_{}_frequency_{}".format(label, ii)
             latex_label = "$f^{}_{}$".format(label, ii)