diff --git a/src/freelunch/optimisers.py b/src/freelunch/optimisers.py
index 61852c0..3de1126 100644
--- a/src/freelunch/optimisers.py
+++ b/src/freelunch/optimisers.py
@@ -403,7 +403,7 @@ def local_motion(self,herd,gen):
         winner, loser = self.winners_and_losers(herd)
         spread = loser[0] - winner[0]
         if spread == 0:
-            warnings.warn(util.KrillSingularityWarning)
+            warnings.warn(util.KrillSingularityWarning())
             spread = 1e-8
         # Alpha stores local [0] and target [1] for each krill 
         alpha = [np.zeros_like(herd[1]), np.zeros_like(herd[1])]