diff --git a/gtsam/hybrid/HybridFactor.cpp b/gtsam/hybrid/HybridFactor.cpp
index 89b1943cd..5582166a3 100644
--- a/gtsam/hybrid/HybridFactor.cpp
+++ b/gtsam/hybrid/HybridFactor.cpp
@@ -54,20 +54,28 @@ HybridFactor::HybridFactor(const KeyVector &keys)
       category_(HybridCategory::Continuous),
       continuousKeys_(keys) {}
 
+/* ************************************************************************ */
+HybridCategory GetCategory(const KeyVector &continuousKeys,
+                           const DiscreteKeys &discreteKeys) {
+  if ((continuousKeys.size() == 0) && (discreteKeys.size() != 0)) {
+    return HybridCategory::Discrete;
+  } else if ((continuousKeys.size() != 0) && (discreteKeys.size() == 0)) {
+    return HybridCategory::Continuous;
+  } else if ((continuousKeys.size() != 0) && (discreteKeys.size() != 0)) {
+    return HybridCategory::Hybrid;
+  } else {
+    // Case where we have no keys. Should never happen.
+    return HybridCategory::None;
+  }
+}
+
 /* ************************************************************************ */
 HybridFactor::HybridFactor(const KeyVector &continuousKeys,
                            const DiscreteKeys &discreteKeys)
     : Base(CollectKeys(continuousKeys, discreteKeys)),
+      category_(GetCategory(continuousKeys, discreteKeys)),
       discreteKeys_(discreteKeys),
-      continuousKeys_(continuousKeys) {
-  if ((continuousKeys.size() == 0) && (discreteKeys.size() != 0)) {
-    category_ = HybridCategory::Discrete;
-  } else if ((continuousKeys.size() != 0) && (discreteKeys.size() == 0)) {
-    category_ = HybridCategory::Continuous;
-  } else {
-    category_ = HybridCategory::Hybrid;
-  }
-}
+      continuousKeys_(continuousKeys) {}
 
 /* ************************************************************************ */
 HybridFactor::HybridFactor(const DiscreteKeys &discreteKeys)
@@ -98,6 +106,9 @@ void HybridFactor::print(const std::string &s,
     case HybridCategory::Hybrid:
       std::cout << "Hybrid ";
       break;
+    case HybridCategory::None:
+      std::cout << "None ";
+      break;
   }
 
   std::cout << "[";
diff --git a/gtsam/hybrid/HybridFactor.h b/gtsam/hybrid/HybridFactor.h
index 2cc7453f4..d0b9bbabe 100644
--- a/gtsam/hybrid/HybridFactor.h
+++ b/gtsam/hybrid/HybridFactor.h
@@ -42,7 +42,7 @@ DiscreteKeys CollectDiscreteKeys(const DiscreteKeys &key1,
                                  const DiscreteKeys &key2);
 
 /// Enum to help with categorizing hybrid factors.
-enum class HybridCategory { Discrete, Continuous, Hybrid };
+enum class HybridCategory { None, Discrete, Continuous, Hybrid };
 
 /**
  * Base class for *truly* hybrid probabilistic factors
@@ -57,7 +57,7 @@ enum class HybridCategory { Discrete, Continuous, Hybrid };
 class GTSAM_EXPORT HybridFactor : public Factor {
  private:
   /// Record what category of HybridFactor this is.
-  HybridCategory category_;
+  HybridCategory category_ = HybridCategory::None;
 
  protected:
   // Set of DiscreteKeys for this factor.