diff --git a/include/ceres/manifold_test_utils.h b/include/ceres/manifold_test_utils.h
index 4872e66..98f4c69 100644
--- a/include/ceres/manifold_test_utils.h
+++ b/include/ceres/manifold_test_utils.h
@@ -28,20 +28,22 @@
 //
 // Author: sameeragarwal@google.com (Sameer Agarwal)
 
+#include <algorithm>
 #include <cmath>
 #include <limits>
 #include <memory>
 #include <type_traits>
 
+#include "Eigen/Core"
 #include "ceres/dynamic_numeric_diff_cost_function.h"
 #include "ceres/internal/eigen.h"
 #include "ceres/manifold.h"
 #include "ceres/numeric_diff_options.h"
-#include "ceres/rotation.h"
 #include "ceres/types.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
+
 namespace ceres {
 
 // Matchers and macros to simplify testing of custom Manifold objects using the
diff --git a/include/ceres/rotation.h b/include/ceres/rotation.h
index ba7f66e..7062ec3 100644
--- a/include/ceres/rotation.h
+++ b/include/ceres/rotation.h
@@ -837,11 +837,11 @@
 }
 
 template <typename Order, typename T>
-inline void QuaternionConjugate(const T q[4], T w[4]) {
-  w[Order::kW] = q[Order::kW];
-  w[Order::kX] = -q[Order::kX];
-  w[Order::kY] = -q[Order::kY];
-  w[Order::kZ] = -q[Order::kZ];
+inline void QuaternionConjugate(const T q[4], T z[4]) {
+  z[Order::kW] = q[Order::kW];
+  z[Order::kX] = -q[Order::kX];
+  z[Order::kY] = -q[Order::kY];
+  z[Order::kZ] = -q[Order::kZ];
 }
 
 // xy = x cross y;
diff --git a/internal/ceres/covariance_impl.cc b/internal/ceres/covariance_impl.cc
index 930711f..b2449f9 100644
--- a/internal/ceres/covariance_impl.cc
+++ b/internal/ceres/covariance_impl.cc
@@ -38,7 +38,10 @@
 #include <utility>
 #include <vector>
 
+#include "Eigen/Core"
+#include "Eigen/Dense"
 #include "Eigen/SVD"
+#include "Eigen/Sparse"
 #include "Eigen/SparseCore"
 #include "Eigen/SparseQR"
 #include "absl/container/flat_hash_set.h"
diff --git a/internal/ceres/invert_psd_matrix.h b/internal/ceres/invert_psd_matrix.h
index dd3a0a3..50b357c 100644
--- a/internal/ceres/invert_psd_matrix.h
+++ b/internal/ceres/invert_psd_matrix.h
@@ -31,7 +31,9 @@
 #ifndef CERES_INTERNAL_INVERT_PSD_MATRIX_H_
 #define CERES_INTERNAL_INVERT_PSD_MATRIX_H_
 
+#include "Eigen/Core"
 #include "Eigen/Dense"
+#include "Eigen/SVD"
 #include "ceres/internal/eigen.h"
 
 namespace ceres::internal {
diff --git a/internal/ceres/rotation_test.cc b/internal/ceres/rotation_test.cc
index 2328114..d7093bc 100644
--- a/internal/ceres/rotation_test.cc
+++ b/internal/ceres/rotation_test.cc
@@ -38,6 +38,7 @@
 #include <string>
 #include <utility>
 
+#include "Eigen/Core"
 #include "absl/log/log.h"
 #include "absl/strings/str_format.h"
 #include "ceres/constants.h"