diff --git a/sumpy/kernel.py b/sumpy/kernel.py
index 1a20ffa85be1cb44c7f87915c5f5d4f0cff6f104..e7864ebe6872300885f0bdc48c5a6de41733f234 100644
--- a/sumpy/kernel.py
+++ b/sumpy/kernel.py
@@ -545,7 +545,7 @@ class StressletKernel(ExpressionKernel):
         key_hash.update(type(self).__name__.encode())
         key_builder.rec(key_hash, (
             self.dim, self.icomp, self.jcomp, self.kcomp, self.viscosity_mu_name,
-            self.stresslet_vector_name))
+            self.viscosity_mu_name))
 
     def __repr__(self):
         return "StressletKnl%dD_%d%d%d" % (self.dim, self.icomp, self.jcomp,