diff --git a/pysisyphus/cos/ChainOfStates.py b/pysisyphus/cos/ChainOfStates.py
index 4adbb100b..4a4f60d50 100644
--- a/pysisyphus/cos/ChainOfStates.py
+++ b/pysisyphus/cos/ChainOfStates.py
@@ -13,7 +13,7 @@
 from scipy.interpolate import interp1d, splprep, splev
 
 from pysisyphus.helpers import align_coords, get_coords_diffs
-from pysisyphus.helpers_pure import hash_arr
+from pysisyphus.helpers_pure import hash_arr, rms
 from pysisyphus.modefollow import geom_lanczos
 
 
@@ -713,22 +713,6 @@ def prepare_opt_cycle(self, last_coords, last_energies, last_forces):
         reset_flag = not already_climbing and self.started_climbing
         return reset_flag, messages
 
-    def rms(self, arr):
-        """Root mean square
-
-        Returns the root mean square of the given array.
-
-        Parameters
-        ----------
-        arr : iterable of numbers
-
-        Returns
-        -------
-        rms : float
-            Root mean square of the given array.
-        """
-        return np.sqrt(np.mean(np.square(arr)))
-
     def compare_image_rms_forces(self, ref_rms):
         """Compare rms(forces) value of an image against a reference value.
 
@@ -740,7 +724,7 @@ def compare_image_rms_forces(self, ref_rms):
         RMS force (rms_force) or from a multiple of the
         RMS force convergence threshold (rms_multiple, default).
         """
-        rms_forces = self.rms(self.forces_list[-1])
+        rms_forces = rms(self.perpendicular_forces)
         # Only start climbing when the COS is fully grown. This
         # attribute may not be defined in all subclasses, so it
         # defaults to True here.
diff --git a/pysisyphus/helpers_pure.py b/pysisyphus/helpers_pure.py
index 656f59fed..6eaccb312 100644
--- a/pysisyphus/helpers_pure.py
+++ b/pysisyphus/helpers_pure.py
@@ -658,5 +658,18 @@ def kill_dir(path):
     path.rmdir()
 
 
-def rms(arr):
+def rms(arr: np.ndarray) -> float:
+    """Root mean square
+
+    Returns the root mean square of the given array.
+
+    Parameters
+    ----------
+    arr : iterable of numbers
+
+    Returns
+    -------
+    rms : float
+        Root mean square of the given array.
+    """
     return np.sqrt(np.mean(arr**2))
diff --git a/tests/test_cos/test_cos.py b/tests/test_cos/test_cos.py
index 679a40dec..d8b78ce2c 100644
--- a/tests/test_cos/test_cos.py
+++ b/tests/test_cos/test_cos.py
@@ -237,7 +237,7 @@ def test_stiff_neb_nfk():
     # plt.show()
 
 
-@pytest.mark.parametrize("climb, ref_cycles", ((True, 209), ("one", 109), (False, 120)))
+@pytest.mark.parametrize("climb, ref_cycles", ((True, 217), ("one", 101), (False, 120)))
 def test_neb_climb(climb, ref_cycles):
     geoms = get_geoms()
 
@@ -273,8 +273,9 @@ def test_cos_image_ts_opt():
     cos_kwargs = {
         "k_min": 0.01,
         "climb": "one",
+        "climb_rms": 0.5,
         "ts_opt": True,
-        "ts_opt_rms": 0.0045,
+        "ts_opt_rms": 0.005,
     }
     cos = NEB(images, **cos_kwargs)