diff --git a/pysindy/optimizers/trapping_sr3.py b/pysindy/optimizers/trapping_sr3.py
index d4d9bca7b..231f797dc 100644
--- a/pysindy/optimizers/trapping_sr3.py
+++ b/pysindy/optimizers/trapping_sr3.py
@@ -341,7 +341,7 @@ def _set_Ptensors(self, r):
             for j in range(r):
                 for k in range(r):
                     for kk in range(N):
-                        if i == kk and j == k:
+                        if i == k and j == kk:
                             PL_tensor_unsym[i, j, k, kk] = 1.0
 
         # Now symmetrize PL