diff --git a/gtsam/linear/ConjugateGradientSolver.h b/gtsam/linear/ConjugateGradientSolver.h
index b09b1a352..ccdab45da 100644
--- a/gtsam/linear/ConjugateGradientSolver.h
+++ b/gtsam/linear/ConjugateGradientSolver.h
@@ -24,20 +24,22 @@
 namespace gtsam {
 
 /**
- * parameters for the conjugate gradient method
+ * Parameters for the Conjugate Gradient method
  */
 class GTSAM_EXPORT ConjugateGradientParameters : public IterativeOptimizationParameters {
 
-public:
+ public:
   typedef IterativeOptimizationParameters Base;
   typedef std::shared_ptr<ConjugateGradientParameters> shared_ptr;
 
+ protected:
   size_t minIterations_;  ///< minimum number of cg iterations
   size_t maxIterations_;  ///< maximum number of cg iterations
   size_t reset_;          ///< number of iterations before reset
   double epsilon_rel_;    ///< threshold for relative error decrease
   double epsilon_abs_;    ///< threshold for absolute error decrease
 
+ public:
   /* Matrix Operation Kernel */
   enum BLASKernel {
     GTSAM = 0,        ///< Jacobian Factor Graph of GTSAM
diff --git a/gtsam/linear/PCGSolver.h b/gtsam/linear/PCGSolver.h
index a6a16f722..cb671f288 100644
--- a/gtsam/linear/PCGSolver.h
+++ b/gtsam/linear/PCGSolver.h
@@ -31,7 +31,7 @@ class VectorValues;
 struct PreconditionerParameters;
 
 /**
- * Parameters for PCG
+ * Parameters for Preconditioned Conjugate Gradient solver.
  */
 struct GTSAM_EXPORT PCGSolverParameters: public ConjugateGradientParameters {
  public:
@@ -91,8 +91,8 @@ public:
  * System class needed for calling preconditionedConjugateGradient
  */
 class GTSAM_EXPORT GaussianFactorGraphSystem {
-  GaussianFactorGraph gfg_;
-  Preconditioner preconditioner_;
+  const GaussianFactorGraph &gfg_;
+  const Preconditioner &preconditioner_;
   KeyInfo keyInfo_;
   std::map<Key, Vector> lambda_;