diff --git a/include/ceres/gradient_problem_solver.h b/include/ceres/gradient_problem_solver.h
index 0676d92..1ed1e4a 100644
--- a/include/ceres/gradient_problem_solver.h
+++ b/include/ceres/gradient_problem_solver.h
@@ -81,7 +81,7 @@
     // Returns true if the options struct has a valid
     // configuration. Returns false otherwise, and fills in *error
     // with a message describing the problem.
-    bool IsValid(string* error) const;
+    bool IsValid(std::string* error) const;
 
     // Minimizer options ----------------------------------------
     LineSearchDirectionType line_search_direction_type;
@@ -269,11 +269,11 @@
 
     // A brief one line description of the state of the solver after
     // termination.
-    string BriefReport() const;
+    std::string BriefReport() const;
 
     // A full multiline description of the state of the solver after
     // termination.
-    string FullReport() const;
+    std::string FullReport() const;
 
     bool IsSolutionUsable() const;
 
@@ -281,7 +281,7 @@
     TerminationType termination_type;
 
     // Reason why the solver terminated.
-    string message;
+    std::string message;
 
     // Cost of the problem (value of the objective function) before
     // the optimization.
diff --git a/include/ceres/internal/port.h b/include/ceres/internal/port.h
index 24eca05..6cee7ba 100644
--- a/include/ceres/internal/port.h
+++ b/include/ceres/internal/port.h
@@ -34,8 +34,6 @@
 // This file needs to compile as c code.
 #ifdef __cplusplus
 
-#include <string>
-
 #include "ceres/internal/config.h"
 
 #if defined(CERES_TR1_MEMORY_HEADER)
@@ -46,10 +44,6 @@
 
 namespace ceres {
 
-// This is necessary to properly handle the case that there is a different
-// "string" implementation in the global namespace.
-using std::string;
-
 #if defined(CERES_TR1_SHARED_PTR)
 using std::tr1::shared_ptr;
 #else
diff --git a/include/ceres/solver.h b/include/ceres/solver.h
index dc06151..cfa2974 100644
--- a/include/ceres/solver.h
+++ b/include/ceres/solver.h
@@ -141,7 +141,7 @@
     // Returns true if the options struct has a valid
     // configuration. Returns false otherwise, and fills in *error
     // with a message describing the problem.
-    bool IsValid(string* error) const;
+    bool IsValid(std::string* error) const;
 
     // Minimizer options ----------------------------------------
 
@@ -683,7 +683,7 @@
     // non-empty if trust_region_minimizer_iterations_to_dump is
     // non-empty and trust_region_problem_dump_format_type is not
     // CONSOLE.
-    string trust_region_problem_dump_directory;
+    std::string trust_region_problem_dump_directory;
     DumpFormatType trust_region_problem_dump_format_type;
 
     // Finite differences options ----------------------------------------------
@@ -755,11 +755,11 @@
 
     // A brief one line description of the state of the solver after
     // termination.
-    string BriefReport() const;
+    std::string BriefReport() const;
 
     // A full multiline description of the state of the solver after
     // termination.
-    string FullReport() const;
+    std::string FullReport() const;
 
     bool IsSolutionUsable() const;
 
@@ -769,7 +769,7 @@
     TerminationType termination_type;
 
     // Reason why the solver terminated.
-    string message;
+    std::string message;
 
     // Cost of the problem (value of the objective function) before
     // the optimization.
diff --git a/include/ceres/types.h b/include/ceres/types.h
index 8915188..c9ee34c 100644
--- a/include/ceres/types.h
+++ b/include/ceres/types.h
@@ -416,65 +416,65 @@
 
 CERES_EXPORT const char* LinearSolverTypeToString(
     LinearSolverType type);
-CERES_EXPORT bool StringToLinearSolverType(string value,
+CERES_EXPORT bool StringToLinearSolverType(std::string value,
                                            LinearSolverType* type);
 
 CERES_EXPORT const char* PreconditionerTypeToString(PreconditionerType type);
-CERES_EXPORT bool StringToPreconditionerType(string value,
+CERES_EXPORT bool StringToPreconditionerType(std::string value,
                                              PreconditionerType* type);
 
 CERES_EXPORT const char* VisibilityClusteringTypeToString(
     VisibilityClusteringType type);
-CERES_EXPORT bool StringToVisibilityClusteringType(string value,
+CERES_EXPORT bool StringToVisibilityClusteringType(std::string value,
                                       VisibilityClusteringType* type);
 
 CERES_EXPORT const char* SparseLinearAlgebraLibraryTypeToString(
     SparseLinearAlgebraLibraryType type);
 CERES_EXPORT bool StringToSparseLinearAlgebraLibraryType(
-    string value,
+    std::string value,
     SparseLinearAlgebraLibraryType* type);
 
 CERES_EXPORT const char* DenseLinearAlgebraLibraryTypeToString(
     DenseLinearAlgebraLibraryType type);
 CERES_EXPORT bool StringToDenseLinearAlgebraLibraryType(
-    string value,
+    std::string value,
     DenseLinearAlgebraLibraryType* type);
 
 CERES_EXPORT const char* TrustRegionStrategyTypeToString(
     TrustRegionStrategyType type);
-CERES_EXPORT bool StringToTrustRegionStrategyType(string value,
+CERES_EXPORT bool StringToTrustRegionStrategyType(std::string value,
                                      TrustRegionStrategyType* type);
 
 CERES_EXPORT const char* DoglegTypeToString(DoglegType type);
-CERES_EXPORT bool StringToDoglegType(string value, DoglegType* type);
+CERES_EXPORT bool StringToDoglegType(std::string value, DoglegType* type);
 
 CERES_EXPORT const char* MinimizerTypeToString(MinimizerType type);
-CERES_EXPORT bool StringToMinimizerType(string value, MinimizerType* type);
+CERES_EXPORT bool StringToMinimizerType(std::string value, MinimizerType* type);
 
 CERES_EXPORT const char* LineSearchDirectionTypeToString(
     LineSearchDirectionType type);
-CERES_EXPORT bool StringToLineSearchDirectionType(string value,
+CERES_EXPORT bool StringToLineSearchDirectionType(std::string value,
                                      LineSearchDirectionType* type);
 
 CERES_EXPORT const char* LineSearchTypeToString(LineSearchType type);
-CERES_EXPORT bool StringToLineSearchType(string value, LineSearchType* type);
+CERES_EXPORT bool StringToLineSearchType(std::string value, LineSearchType* type);
 
 CERES_EXPORT const char* NonlinearConjugateGradientTypeToString(
     NonlinearConjugateGradientType type);
 CERES_EXPORT bool StringToNonlinearConjugateGradientType(
-    string value,
+    std::string value,
     NonlinearConjugateGradientType* type);
 
 CERES_EXPORT const char* LineSearchInterpolationTypeToString(
     LineSearchInterpolationType type);
 CERES_EXPORT bool StringToLineSearchInterpolationType(
-    string value,
+    std::string value,
     LineSearchInterpolationType* type);
 
 CERES_EXPORT const char* CovarianceAlgorithmTypeToString(
     CovarianceAlgorithmType type);
 CERES_EXPORT bool StringToCovarianceAlgorithmType(
-    string value,
+    std::string value,
     CovarianceAlgorithmType* type);
 
 CERES_EXPORT const char* TerminationTypeToString(TerminationType type);