diff --git a/interpax/_spline.py b/interpax/_spline.py
index 6013582..c44230d 100644
--- a/interpax/_spline.py
+++ b/interpax/_spline.py
@@ -1072,14 +1072,23 @@ def derivative1():
 def _make_periodic(xq: jax.Array, x: jax.Array, period: float, axis: int, *arrs):
     """Make arrays periodic along a specified axis."""
     period = abs(period)
-    xq = jnp.where(jnp.logical_or(xq > period, xq < 0), xq % period, xq)
-    x = jnp.where(jnp.logical_or(x > period, x < 0), x % period, x)
+    xq = xq % period
+    x = x % period
     i = jnp.argsort(x)
     x = x[i]
+    x = jnp.concatenate([x[-1:] - period, x, x[:1] + period])
     arrs = list(arrs)
     for k in range(len(arrs)):
         if arrs[k] is not None:
             arrs[k] = jnp.take(arrs[k], i, axis, mode="wrap")
+            arrs[k] = jnp.concatenate(
+                [
+                    jnp.take(arrs[k], jnp.array([-1]), axis),
+                    arrs[k],
+                    jnp.take(arrs[k], jnp.array([0]), axis),
+                ],
+                axis=axis,
+            )
     return (xq, x, *arrs)