diff --git a/gtsam/hybrid/HybridFactorGraph.cpp b/gtsam/hybrid/HybridFactorGraph.cpp
index f7b96f694..f5a7bcdfe 100644
--- a/gtsam/hybrid/HybridFactorGraph.cpp
+++ b/gtsam/hybrid/HybridFactorGraph.cpp
@@ -49,15 +49,6 @@ KeySet HybridFactorGraph::discreteKeySet() const {
   return keys;
 }
 
-/* ************************************************************************* */
-std::unordered_map<Key, DiscreteKey> HybridFactorGraph::discreteKeyMap() const {
-  std::unordered_map<Key, DiscreteKey> result;
-  for (const DiscreteKey& k : discreteKeys()) {
-    result[k.first] = k;
-  }
-  return result;
-}
-
 /* ************************************************************************* */
 const KeySet HybridFactorGraph::continuousKeySet() const {
   KeySet keys;
diff --git a/gtsam/hybrid/HybridFactorGraph.h b/gtsam/hybrid/HybridFactorGraph.h
index 1830d44ab..79f2a7af1 100644
--- a/gtsam/hybrid/HybridFactorGraph.h
+++ b/gtsam/hybrid/HybridFactorGraph.h
@@ -38,7 +38,7 @@ using SharedFactor = std::shared_ptr<Factor>;
 class GTSAM_EXPORT HybridFactorGraph : public FactorGraph<Factor> {
  public:
   using Base = FactorGraph<Factor>;
-  using This = HybridFactorGraph;              ///< this class
+  using This = HybridFactorGraph;            ///< this class
   using shared_ptr = std::shared_ptr<This>;  ///< shared_ptr to This
 
   using Values = gtsam::Values;  ///< backwards compatibility
@@ -69,9 +69,6 @@ class GTSAM_EXPORT HybridFactorGraph : public FactorGraph<Factor> {
   /// Get all the discrete keys in the factor graph, as a set of Keys.
   KeySet discreteKeySet() const;
 
-  /// Get a map from Key to corresponding DiscreteKey.
-  std::unordered_map<Key, DiscreteKey> discreteKeyMap() const;
-
   /// Get all the continuous keys in the factor graph.
   const KeySet continuousKeySet() const;
 
diff --git a/gtsam/hybrid/HybridGaussianFactorGraph.cpp b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
index c44fc4f1d..a7a6eee5a 100644
--- a/gtsam/hybrid/HybridGaussianFactorGraph.cpp
+++ b/gtsam/hybrid/HybridGaussianFactorGraph.cpp
@@ -312,8 +312,8 @@ using Result = std::pair<std::shared_ptr<GaussianConditional>,
                          GaussianMixtureFactor::sharedFactor>;
 
 /**
- * Compute the probability q(μ;m) = exp(-error(μ;m)) * sqrt(det(2π Σ_m)
- * from the residual error at the mean μ.
+ * Compute the probability p(μ;m) = exp(-error(μ;m)) * sqrt(det(2π Σ_m)
+ * from the residual error ||b||^2 at the mean μ.
  * The residual error contains no keys, and only
  * depends on the discrete separator if present.
  */
@@ -523,19 +523,9 @@ EliminateHybrid(const HybridGaussianFactorGraph &factors,
         std::inserter(continuousSeparator, continuousSeparator.begin()));
 
     // Similarly for the discrete separator.
-    auto discreteKeySet = factors.discreteKeySet();
-    // Use set-difference to get the difference in keys
-    KeySet discreteSeparatorSet;
-    std::set_difference(
-        discreteKeySet.begin(), discreteKeySet.end(), frontalKeysSet.begin(),
-        frontalKeysSet.end(),
-        std::inserter(discreteSeparatorSet, discreteSeparatorSet.begin()));
-    // Convert from set of keys to set of DiscreteKeys
-    std::set<DiscreteKey> discreteSeparator;
-    auto discreteKeyMap = factors.discreteKeyMap();
-    for (auto key : discreteSeparatorSet) {
-      discreteSeparator.insert(discreteKeyMap.at(key));
-    }
+    // Since we eliminate all continuous variables first,
+    // the discrete separator will be *all* the discrete keys.
+    std::set<DiscreteKey> discreteSeparator = factors.discreteKeys();
 
     return hybridElimination(factors, frontalKeys, continuousSeparator,
                              discreteSeparator);
diff --git a/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp b/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp
index 139b50e2a..b2a4981f3 100644
--- a/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp
+++ b/gtsam/hybrid/tests/testGaussianMixtureFactor.cpp
@@ -434,12 +434,12 @@ static HybridBayesNet CreateBayesNet(double mu0, double mu1, double sigma0,
 
 /* ************************************************************************* */
 /**
- * Test a model P(x0)P(z0|x0)P(x1|x0,m1)P(z1|x1)P(m1).
+ * Test a model P(z0|x0)P(x1|x0,m1)P(z1|x1)P(m1).
  *
  * P(f01|x1,x0,m1) has different means and same covariance.
  *
  * Converting to a factor graph gives us
- * P(x0)ϕ(x0)ϕ(x1,x0,m1)ϕ(x1)P(m1)
+ * ϕ(x0)ϕ(x1,x0,m1)ϕ(x1)P(m1)
  *
  * If we only have a measurement on z0, then
  * the probability of m1 should be 0.5/0.5.
@@ -488,12 +488,12 @@ TEST(GaussianMixtureFactor, TwoStateModel) {
 
 /* ************************************************************************* */
 /**
- * Test a model P(x0)P(z0|x0)P(x1|x0,m1)P(z1|x1)P(m1).
+ * Test a model P(z0|x0)P(x1|x0,m1)P(z1|x1)P(m1).
  *
  * P(f01|x1,x0,m1) has different means and different covariances.
  *
  * Converting to a factor graph gives us
- * P(x0)ϕ(x0)ϕ(x1,x0,m1)ϕ(x1)P(m1)
+ * ϕ(x0)ϕ(x1,x0,m1)ϕ(x1)P(m1)
  *
  * If we only have a measurement on z0, then
  * the P(m1) should be 0.5/0.5.