diff --git a/gtsam/hybrid/MixtureFactor.h b/gtsam/hybrid/MixtureFactor.h
index fc1a9a2b8..5285dd191 100644
--- a/gtsam/hybrid/MixtureFactor.h
+++ b/gtsam/hybrid/MixtureFactor.h
@@ -162,14 +162,20 @@ class MixtureFactor : public HybridFactor {
   }
 
   /// Error for HybridValues is not provided for nonlinear hybrid factor.
-  double error(const HybridValues &values) const override {
+  double error(const HybridValues& values) const override {
     throw std::runtime_error(
         "MixtureFactor::error(HybridValues) not implemented.");
   }
 
+  /**
+   * @brief Get the dimension of the factor (number of rows on linearization).
+   * Returns the dimension of the first component factor.
+   * @return size_t
+   */
   size_t dim() const {
-    // TODO(Varun)
-    throw std::runtime_error("MixtureFactor::dim not implemented.");
+    const auto assignments = DiscreteValues::CartesianProduct(discreteKeys_);
+    auto factor = factors_(assignments.at(0));
+    return factor->dim();
   }
 
   /// Testable
diff --git a/gtsam/hybrid/tests/testMixtureFactor.cpp b/gtsam/hybrid/tests/testMixtureFactor.cpp
index fe3212eda..9e4d66bf2 100644
--- a/gtsam/hybrid/tests/testMixtureFactor.cpp
+++ b/gtsam/hybrid/tests/testMixtureFactor.cpp
@@ -70,8 +70,7 @@ MixtureFactor
 }
 
 /* ************************************************************************* */
-// Test the error of the MixtureFactor
-TEST(MixtureFactor, Error) {
+static MixtureFactor getMixtureFactor() {
   DiscreteKey m1(1, 2);
 
   double between0 = 0.0;
@@ -86,7 +85,13 @@ TEST(MixtureFactor, Error) {
       boost::make_shared<BetweenFactor<double>>(X(1), X(2), between1, model);
   std::vector<NonlinearFactor::shared_ptr> factors{f0, f1};
 
-  MixtureFactor mixtureFactor({X(1), X(2)}, {m1}, factors);
+  return MixtureFactor({X(1), X(2)}, {m1}, factors);
+}
+
+/* ************************************************************************* */
+// Test the error of the MixtureFactor
+TEST(MixtureFactor, Error) {
+  auto mixtureFactor = getMixtureFactor();
 
   Values continuousValues;
   continuousValues.insert<double>(X(1), 0);
@@ -94,6 +99,7 @@ TEST(MixtureFactor, Error) {
 
   AlgebraicDecisionTree<Key> error_tree = mixtureFactor.error(continuousValues);
 
+  DiscreteKey m1(1, 2);
   std::vector<DiscreteKey> discrete_keys = {m1};
   std::vector<double> errors = {0.5, 0};
   AlgebraicDecisionTree<Key> expected_error(discrete_keys, errors);
@@ -101,6 +107,13 @@ TEST(MixtureFactor, Error) {
   EXPECT(assert_equal(expected_error, error_tree));
 }
 
+/* ************************************************************************* */
+// Test dim of the MixtureFactor
+TEST(MixtureFactor, Dim) {
+  auto mixtureFactor = getMixtureFactor();
+  EXPECT_LONGS_EQUAL(1, mixtureFactor.dim());
+}
+
 /* ************************************************************************* */
 int main() {
   TestResult tr;