diff --git a/gtsam/hybrid/HybridFactor.h b/gtsam/hybrid/HybridFactor.h
index 39a72eb26..fc91e0838 100644
--- a/gtsam/hybrid/HybridFactor.h
+++ b/gtsam/hybrid/HybridFactor.h
@@ -56,9 +56,11 @@ class GTSAM_EXPORT HybridFactor : public Factor {
   /// Enum to help with categorizing hybrid factors.
   enum class Category { None, Discrete, Continuous, Hybrid };
 
- protected:
+ private:
   /// Record what category of HybridFactor this is.
   Category category_ = Category::None;
+
+ protected:
   // Set of DiscreteKeys for this factor.
   DiscreteKeys discreteKeys_;
   /// Record continuous keys for book-keeping
@@ -140,10 +142,6 @@ class GTSAM_EXPORT HybridFactor : public Factor {
 
   /// @}
 
- protected:
-  /// protected constructor to initialize the category
-  HybridFactor(Category category) : category_(category) {}
-
  private:
 #ifdef GTSAM_ENABLE_BOOST_SERIALIZATION
   /** Serialization function */