diff --git a/internal/ceres/lapack.cc b/internal/ceres/lapack.cc
index a3d9980..6cf2f6b 100644
--- a/internal/ceres/lapack.cc
+++ b/internal/ceres/lapack.cc
@@ -70,7 +70,7 @@
     int num_rows,
     const double* in_lhs,
     double* rhs_and_solution,
-    string* message) {
+    std::string* message) {
 #ifdef CERES_NO_LAPACK
   LOG(FATAL) << "Ceres was built without a BLAS library.";
   return LINEAR_SOLVER_FATAL_ERROR;
@@ -151,7 +151,7 @@
     int work_size,
     double* work,
     double* rhs_and_solution,
-    string* message) {
+    std::string* message) {
 #ifdef CERES_NO_LAPACK
   LOG(FATAL) << "Ceres was built without a LAPACK library.";
   return LINEAR_SOLVER_FATAL_ERROR;