diff --git a/gtsam/navigation/CombinedImuFactor.h b/gtsam/navigation/CombinedImuFactor.h
index e1a38bc91..42180ca04 100644
--- a/gtsam/navigation/CombinedImuFactor.h
+++ b/gtsam/navigation/CombinedImuFactor.h
@@ -156,7 +156,7 @@ public:
    *  @param biasHat Current estimate of acceleration and rotation rate biases
    */
   PreintegratedCombinedMeasurements(
-      const boost::shared_ptr<Params>& p,
+      const boost::shared_ptr<const Params>& p,
       const imuBias::ConstantBias& biasHat = imuBias::ConstantBias())
       : PreintegrationType(p, biasHat) {
     preintMeasCov_.setZero();
@@ -184,7 +184,7 @@ public:
   void resetIntegration() override;
 
   /// const reference to params, shadows definition in base class
-  Params& p() const { return *boost::static_pointer_cast<Params>(this->p_); }
+  const Params& p() const { return *boost::static_pointer_cast<const Params>(this->p_); }
   /// @}
 
   /// @name Access instance variables
diff --git a/gtsam/navigation/PreintegrationBase.cpp b/gtsam/navigation/PreintegrationBase.cpp
index 45560f34d..1c8fdd760 100644
--- a/gtsam/navigation/PreintegrationBase.cpp
+++ b/gtsam/navigation/PreintegrationBase.cpp
@@ -28,7 +28,7 @@ using namespace std;
 namespace gtsam {
 
 //------------------------------------------------------------------------------
-PreintegrationBase::PreintegrationBase(const boost::shared_ptr<Params>& p,
+PreintegrationBase::PreintegrationBase(const boost::shared_ptr<const Params>& p,
                                        const Bias& biasHat)
     : p_(p), biasHat_(biasHat), deltaTij_(0.0) {
 }
diff --git a/gtsam/navigation/PreintegrationBase.h b/gtsam/navigation/PreintegrationBase.h
index 3ef7ad5df..e4edbe562 100644
--- a/gtsam/navigation/PreintegrationBase.h
+++ b/gtsam/navigation/PreintegrationBase.h
@@ -44,7 +44,7 @@ class GTSAM_EXPORT PreintegrationBase {
   typedef PreintegrationParams Params;
 
  protected:
-  boost::shared_ptr<Params> p_;
+  boost::shared_ptr<const Params> p_;
 
   /// Acceleration and gyro bias used for preintegration
   Bias biasHat_;
@@ -67,7 +67,7 @@ class GTSAM_EXPORT PreintegrationBase {
    *  @param p    Parameters, typically fixed in a single application
    *  @param bias Current estimate of acceleration and rotation rate biases
    */
-  PreintegrationBase(const boost::shared_ptr<Params>& p,
+  PreintegrationBase(const boost::shared_ptr<const Params>& p,
       const imuBias::ConstantBias& biasHat = imuBias::ConstantBias());
 
   /// @}
@@ -88,13 +88,13 @@ class GTSAM_EXPORT PreintegrationBase {
   }
 
   /// shared pointer to params
-  const boost::shared_ptr<Params>& params() const {
+  const boost::shared_ptr<const Params>& params() const {
     return p_;
   }
 
   /// const reference to params
   const Params& p() const {
-    return *boost::static_pointer_cast<Params>(p_);
+    return *p_;
   }
 
   /// @}
diff --git a/gtsam/navigation/TangentPreintegration.cpp b/gtsam/navigation/TangentPreintegration.cpp
index 56d7aa6d3..0d39242b7 100644
--- a/gtsam/navigation/TangentPreintegration.cpp
+++ b/gtsam/navigation/TangentPreintegration.cpp
@@ -24,7 +24,7 @@ using namespace std;
 namespace gtsam {
 
 //------------------------------------------------------------------------------
-TangentPreintegration::TangentPreintegration(const boost::shared_ptr<Params>& p,
+TangentPreintegration::TangentPreintegration(const boost::shared_ptr<const Params>& p,
     const Bias& biasHat) :
     PreintegrationBase(p, biasHat) {
   resetIntegration();
diff --git a/gtsam/navigation/TangentPreintegration.h b/gtsam/navigation/TangentPreintegration.h
index 1b51b4e1e..183c7262e 100644
--- a/gtsam/navigation/TangentPreintegration.h
+++ b/gtsam/navigation/TangentPreintegration.h
@@ -50,7 +50,7 @@ public:
    *  @param p    Parameters, typically fixed in a single application
    *  @param bias Current estimate of acceleration and rotation rate biases
    */
-  TangentPreintegration(const boost::shared_ptr<Params>& p,
+  TangentPreintegration(const boost::shared_ptr<const Params>& p,
       const imuBias::ConstantBias& biasHat = imuBias::ConstantBias());
 
   /// Virtual destructor