diff --git a/xacc/optimizer/mlpack/mlpack_optimizer.cpp b/xacc/optimizer/mlpack/mlpack_optimizer.cpp
index 948d6ea73..6b32f82b4 100644
--- a/xacc/optimizer/mlpack/mlpack_optimizer.cpp
+++ b/xacc/optimizer/mlpack/mlpack_optimizer.cpp
@@ -192,7 +192,7 @@ OptResult MLPACKOptimizer::optimize(OptFunction &function) {
     if (options.keyExists<double>("mlpack-cmaes-lower-bound")) {
       lower = options.get<double>("mlpack-cmaes-lower-bound");
     }
-    CMAES<> optimizer(lambda, upper, lower, 1, maxiter, tol);
+    CMAES<> optimizer(lambda, lower, upper, 1, maxiter, tol);
     results = optimizer.Optimize(f, coordinates);
 #else
     xacc::error("Cannot run mlpack cmaes algorithm, lapack not found.");
@@ -240,4 +240,4 @@ OptResult MLPACKOptimizer::optimize(OptFunction &function) {
 
 } // namespace xacc
 
-REGISTER_OPTIMIZER(xacc::MLPACKOptimizer)
\ No newline at end of file
+REGISTER_OPTIMIZER(xacc::MLPACKOptimizer)