diff --git a/sensor/tag_based_pnp_calibrator/src/calibration_estimator.cpp b/sensor/tag_based_pnp_calibrator/src/calibration_estimator.cpp
index 431101c4..bea31c35 100644
--- a/sensor/tag_based_pnp_calibrator/src/calibration_estimator.cpp
+++ b/sensor/tag_based_pnp_calibrator/src/calibration_estimator.cpp
@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <Eigen/Dense>  // note: this header must come before <opencv2/core/eigen.hpp>
 #include <opencv2/core.hpp>
 #include <opencv2/core/eigen.hpp>
 #include <opencv2/imgproc.hpp>