diff --git a/gtsam/linear/PCGSolver.h b/gtsam/linear/PCGSolver.h
index 42bb3fccc..17cc2d3db 100644
--- a/gtsam/linear/PCGSolver.h
+++ b/gtsam/linear/PCGSolver.h
@@ -42,7 +42,7 @@ struct GTSAM_EXPORT PCGSolverParameters : public ConjugateGradientParameters {
   PCGSolverParameters() {}
 
   PCGSolverParameters(
-      const std::shared_ptr<PreconditionerParameters> preconditioner)
+      const std::shared_ptr<PreconditionerParameters> &preconditioner)
       : preconditioner(preconditioner) {}
 
   void print(std::ostream &os) const override;