diff --git a/src/harmonicenergystiffness.hh b/src/harmonicenergystiffness.hh
index 509ab6c1983de6caba9e3c7081abb6b30740e068..3440b5f8e2319a8b91a9876a077b2dff8ba1662f 100644
--- a/src/harmonicenergystiffness.hh
+++ b/src/harmonicenergystiffness.hh
@@ -63,7 +63,7 @@ energy(const Entity& element,
         // The derivative of the function defined on the actual element
         Dune::FieldMatrix<double, TargetSpace::EmbeddedTangentVector::size, gridDim> derivative(0);
 
-        for (int comp=0; comp<referenceDerivative.N(); comp++)
+        for (size_t comp=0; comp<referenceDerivative.N(); comp++)
             jacobianInverseTransposed.umv(referenceDerivative[comp], derivative[comp]);
 
 #if 0