diff --git a/cpp/Cal3_S2.cpp b/cpp/Cal3_S2.cpp
index a3df39934..5e72f8d37 100644
--- a/cpp/Cal3_S2.cpp
+++ b/cpp/Cal3_S2.cpp
@@ -13,7 +13,7 @@ namespace gtsam {
 using namespace std;
 
 /* ************************************************************************* */
-void Cal3_S2::load(std::string path) {
+void Cal3_S2::load(const std::string path) {
 	char buffer[200];
 	buffer[0] = 0;
 	sprintf(buffer, "%s/calibration_info.txt", path.c_str());
diff --git a/cpp/Cal3_S2.h b/cpp/Cal3_S2.h
index ccda5c2bd..6f6349ce3 100644
--- a/cpp/Cal3_S2.h
+++ b/cpp/Cal3_S2.h
@@ -41,7 +41,7 @@ namespace gtsam {
 		/**
 		 * load calibration from location (default name is calibration_info.txt)
 		 */
-		void load(std::string path);
+		void load(const std::string path);
 
 		/**
 		 * Given 5-dim tangent vector, create new calibration